Unprecedented serial interface compatibility. Hard drive interfaces: SCSI, SAS, Firewire, IDE, SATA What are sas drives

With the advent of a sufficiently large number of Serial Attached SCSI (SAS) peripherals, we can state the beginning of the transition of the corporate environment to the rails of the new technology. But SAS is not only a recognized successor to UltraSCSI technology, but also opens up new areas of use, raising the scalability of systems downright to unthinkable heights. We decided to demonstrate the potential of SAS by taking a closer look at the technology, host adapters, hard drives, and storage systems.

SAS is not a completely new technology: it takes the best of both worlds. The first part of SAS is about serial communication, which requires less physical wires and pins. The transition from parallel to serial transmission made it possible to get rid of the bus. Although the current SAS specifications define throughput at 300 MB/s per port, which is less than 320 MB/s for UltraSCSI, replacing a shared bus with a point-to-point connection is a significant advantage. The second part of SAS is the SCSI protocol, which remains powerful and popular.

SAS can also use a large set types of RAID. Giants such as Adaptec or LSI Logic offer an advanced set of features for expansion, migration, nesting, and other features in their products, including distributed RAID arrays across multiple controllers and drives.

Finally, most of the actions mentioned today are already performed "on the fly". Here we should note excellent products AMCC/3Ware , Areca and Broadcom/Raidcore, which allowed the transfer of enterprise-class features to SATA spaces.

Compared to SATA, the traditional SCSI implementation is losing ground on all fronts except in high-end enterprise solutions. SATA offers suitable hard drives, has a good price and a wide range of decisions. And let's not forget another "smart" feature of SAS: it easily gets along with existing SATA infrastructures, since SAS host adapters easily work with SATA drives. But the SAS drive cannot be connected to the SATA adapter.

Source: Adaptec.

First, it seems to us, we should turn to the history of SAS. The SCSI standard (stands for "small computer system interface") has always been regarded as a professional bus for connecting drives and some other devices to computers. Hard drives for servers and workstations still use SCSI technology. Unlike the mass ATA standard, which allows only two drives to be connected to one port, SCSI allows up to 15 devices to be connected on one bus and offers a powerful command protocol. Devices must have a unique SCSI ID, which can be assigned either manually or through the SCAM (SCSI Configuration Automatically) protocol. Because the device IDs for the busses of two or more SCSI adapters may not be unique, Logical Unit Numbers (LUNs) have been added to help identify devices in complex SCSI environments.

SCSI hardware is more flexible and reliable than ATA (this standard is also called IDE, Integrated Drive Electronics). Devices can be connected both inside the computer and outside, and the cable length can be up to 12 m, if it is properly terminated (in order to avoid signal reflections). As SCSI has evolved, numerous standards have emerged that specify different bus widths, clock frequency, connectors and signal voltage (Fast, Wide, Ultra, Ultra Wide, Ultra2, Ultra2 Wide, Ultra3, Ultra320 SCSI). Luckily, they all use the same set of commands.

Any SCSI communication is established between the initiator (host adapter) sending commands and the target drive responding to them. Immediately after receiving a set of commands, the target drive sends a so-called sense code (state: busy, error or free), by which the initiator will know whether he will receive the desired response or not.

The SCSI protocol specifies almost 60 different commands. They are divided into four categories: non-data, bi-directional, read data, and write data.

The limitations of SCSI start to show up when you add drives to the bus. Today it is hardly possible to find a hard drive that can fully load the 320 MB / s throughput of Ultra320 SCSI. But five or more drives on the same bus is another matter entirely. An option would be to add a second host adapter for load balancing, but this comes at a cost. Cables are also a problem: twisted 80-wire cables are very expensive. If you also want to get a "hot swap" of drives, that is, an easy replacement of a failed drive, then special equipment (backplane) is required.

Of course, it's best to place the drives in separate fixtures or modules, which are usually hot swappable along with other nice control features. As a result, there are more professional SCSI solutions on the market. But they all cost a lot, which is why the SATA standard has developed so rapidly in recent years. And although SATA will never meet the needs of high-end enterprise systems, this standard perfectly complements SAS in creating new scalable solutions for network environments next generation.

SAS does not use a common bus for multiple devices. Source: Adaptec.

SATA

On the left is the SATA connector for data transfer. On the right is the power connector. There are enough pins to supply 3.3V, 5V, and 12V voltages to each SATA drive.

The SATA standard has been on the market for several years, and today it has reached its second generation. SATA I featured 1.5 Gb/s throughput with two serial connections using low-voltage differential signaling. The physical layer uses 8/10 bit encoding (10 actual bits for 8 bits of data), which accounts for the maximum interface throughput of 150 MB/s. After the transition of SATA to a speed of 300 MB / s, many began to call new standard SATA II, although when standardized SATA-IO(International Organization) planned to add more features first and then call it SATA II. Hence the latest specification is called SATA 2.5, it includes SATA extensions such as Native Command Queuing(NCQ) and eSATA (external SATA), port multipliers (up to four drives per port), etc. But additional SATA features are optional for both the controller and the hard drive itself.

Let's hope that in 2007 SATA III at 600 MB / s will still be released.

Where parallel ATA (UltraATA) cables were limited to 46cm, SATA cables can be up to 1m long, and for eSATA twice that. Instead of 40 or 80 wires, serial transmission requires only a few pins. Therefore, SATA cables are very narrow, easy to route inside a computer case, and don't obstruct airflow as much. A single device relies on a SATA port, making it a point-to-point interface.

SATA connectors for data and power provide separate plugs.

SAS

The signaling protocol here is the same as that of SATA. Source: Adaptec.

A nice feature of Serial Attached SCSI is that the technology supports both SCSI and SATA, as a result of which SAS or SATA drives (or both standards) can be connected to SAS controllers. However, SAS drives cannot work with SATA controllers due to the use of the Serial SCSI Protocol (SSP). Like SATA, SAS follows the point-to-point connection principle for drives (300 MB/s today), and thanks to SAS expanders (or expanders, expanders), more drives can be connected than are available SAS ports. SAS hard drives support two ports, each with its own unique SAS ID, so you can use two physical connections to provide redundancy - connect the drive to two different hosts. Thanks to STP (SATA Tunneling Protocol), SAS controllers can communicate with SATA drives connected to the expander.

Source: Adaptec.

Source: Adaptec.

Source: Adaptec.

Of course, the only physical connection of the SAS expander to the host controller can be considered a "bottleneck", so wide SAS ports are provided in the standard. A wide port groups multiple SAS connections into a single link between any two SAS devices (usually between a host controller and an extender/expander). The number of connections within the connection can be increased, it all depends on the requirements imposed. But redundant connections are not supported, nor are any loops or rings allowed.

Source: Adaptec.

Future implementations of SAS will add 600 and 1200 MB/s bandwidth per port. Of course, the performance of hard drives will not increase in the same proportion, but it will be more convenient to use expanders on a small number of ports.

Devices called "Fan Out" and "Edge" are expanders. But only the main Fan Out expander can work with the SAS domain (see 4x connection in the center of the diagram). Up to 128 physical connections are allowed per Edge expander, and you can use wide ports and/or connect other expanders/drives. The topology can be quite complex, but at the same time flexible and powerful. Source: Adaptec.

Source: Adaptec.

The backplane is the basic building block of any storage system that needs to be hot pluggable. Therefore, SAS expanders often involve powerful rigs (both in a single case and not). Typically, a single link is used to connect a simple snap-in to a host adapter. Expanders with built-in snap-ins, of course, rely on multi-channel connections.

Three types of cables and connectors have been developed for SAS. SFF-8484 is a multicore internal cable that connects the host adapter to the equipment. In principle, the same can be achieved by branching this cable at one end into several separate SAS connectors (see illustration below). SFF-8482 is a connector through which the drive is connected to a single SAS interface. Finally, the SFF-8470 is an external multicore cable, up to six meters long.

Source: Adaptec.

SFF-8470 cable for external multilink SAS connections.

Multicore cable SFF-8484. Four SAS channels/ports pass through one connector.

SFF-8484 cable that allows you to connect four SATA drives.

SAS as part of SAN solutions

Why do we need all this information? Most users will not come close to the SAS topology we discussed above. But SAS is more than a next-generation interface for professional hard drives, although it is ideal for building simple and complex RAID arrays based on one or more RAID controllers. SAS is capable of more. This is a point-to-point serial interface that scales easily as you add more links between any two SAS devices. SAS drives come with two ports, so you can connect one port through an expander to a host system and then create a backup path to another host system (or another expander).

Communication between SAS adapters and expanders (as well as between two expanders) can be as wide as there are available SAS ports. Expanders are usually rack-mounted systems that can accommodate a large number of drives, and the possible connection of SAS to a higher device in the hierarchy (for example, a host controller) is limited only by the capabilities of the expander.

With a rich and functional infrastructure, SAS allows you to create complex storage topologies, rather than dedicated hard drives or separate network storage. In this case, "complicated" should not mean that it is difficult to work with such a topology. SAS configurations consist of simple disk rigs or use expanders. Any SAS link can be scaled up or down depending on bandwidth requirements. You can use both powerful SAS hard drives and high-capacity SATA models. Together with powerful RAID controllers, you can easily set up, expand or reconfigure data arrays - both in terms of the RAID level and the hardware side.

All of this becomes even more important when you consider how fast corporate storage is growing. Today everyone is talking about SAN - storage area network. It implies a decentralized organization of a data storage subsystem with traditional servers using physically remote storages. A slightly modified SCSI protocol is launched over existing Gigabit Ethernet or Fiber Channel networks, encapsulated in Ethernet packets (iSCSI - Internet SCSI). A system that runs from a single hard drive to complex nested RAID arrays becomes a so-called target (target) and is tied to an initiator (host system, initiator), which treats the target as if it were just a physical element.

iSCSI, of course, allows you to create a strategy for the development of storage, data organization or access control. We get another level of flexibility by removing storage directly attached to servers, allowing any storage subsystem to become an iSCSI target. Moving to remote storage makes the system independent of storage servers (a dangerous point of failure) and improves the manageability of the hardware. From a programmatic point of view, the storage is still "inside" the server. The iSCSI target and initiator can be nearby, on different floors, in different rooms or buildings - it all depends on the quality and speed of the IP connection between them. From this point of view, it is important to note that the SAN is ill-suited to the requirements of operational available applications like databases.

2.5" SAS hard drives

2.5" hard drives for the professional sector are still perceived as a novelty. We have been reviewing the first such drive from Seagate for quite some time - 2.5" Ultra320 Savvio who left a good impression. All 2.5" SCSI drives use a 10,000 RPM spindle speed, but they fall short of the performance levels of 3.5" hard drives with the same spindle speed. The fact is that the outer tracks of 3.5 "models rotate at a higher linear speed, which provides a higher data transfer rate.

The advantage of small hard drives lies not in capacity: today, for them, the maximum is still 73 GB, while in 3.5 "enterprise-class hard drives we already get 300 GB. In many areas, the ratio of performance to physical volume occupied is very important or energy efficiency. The more hard drives you use, the more performance you reap - paired with the appropriate infrastructure, of course. At the same time, 2.5" hard drives consume almost half as much energy as 3.5" competitors. If we consider the ratio performance per watt (I/O operations per watt), the 2.5" form factor gives very good results.

If you need capacity first and foremost, 3.5" 10,000 rpm drives are unlikely to be the best choice. The fact is that 3.5" SATA hard drives provide 66% more capacity (500 instead of 300 GB per hard drive), leaving the performance level acceptable. Many hard drive manufacturers offer SATA models for 24/7 operation, and the price of drives Reliability problems can be solved by purchasing spare (spare) drives for immediate replacement in the array.

The MAY line represents Fujitsu's current generation of 2.5" drives for the professional sector. The rotation speed is 10,025 rpm, and the capacities are 36.7 and 73.5 GB. All drives come with 8 MB cache and give an average read seek time 4.0 ms and 4.5 ms writes As we already mentioned, a nice feature of 2.5" hard drives is reduced power consumption. Usually one 2.5" hard drive saves at least 60% of energy compared to a 3.5" drive.

3.5" SAS hard drives

The MAX is Fujitsu's current line of high performance 15,000 rpm hard drives. So the name fits perfectly. Unlike 2.5" drives, here we get a whopping 16MB of cache and a short average seek time of 3.3ms for reads and 3.8ms for writes. Fujitsu offers 36.7GB, 73.4GB, and 146GB models. GB (with one, two and four plates).

Fluid dynamic bearings have made their way to enterprise-class hard drives, so the new models are significantly quieter than the previous ones at 15,000 rpm. Of course, such hard drives should be properly cooled, and the equipment provides this too.

Hitachi Global Storage Technologies also offers its own line of high performance solutions. The UltraStar 15K147 runs at 15,000 rpm and has a 16 MB cache, just like the Fujitsu drives, but the platter configuration is different. The 36.7 GB model uses two platters instead of one, while the 73.4 GB model uses three platters instead of two. This indicates a lower data density, but such a design, in fact, allows you to not use the inner, slowest areas of the plates. As a result, the heads have to move less, which gives a better average access time.

Hitachi also offers 36.7GB, 73.4GB, and 147GB models with a claimed seek (read) time of 3.7ms.

Although Maxtor has already become part of Seagate, the company's product lines are still preserved. The manufacturer offers 36, 73 and 147 GB models, all of which feature a 15,000 rpm spindle speed and 16 MB cache. The company claims an average seek time of 3.4ms for reads and 3.8ms for writes.

The Cheetah has long been associated with high performance hard drives. Seagate was able to instill a similar association with the release of the Barracuda in the desktop segment, offering the first 7200 RPM desktop drive in 2000.

Available in 36.7 GB, 73.4 GB and 146.8 GB models. All of them are distinguished by a spindle speed of 15,000 rpm and an 8 MB cache. The average seek time for reading is 3.5 ms and for writing 4.0 ms.

Host adapters

Unlike SATA controllers, SAS components can only be found on motherboards ah server class or as expansion cards for PCI-X or PCI Express. If we take it a step further and look at RAID controllers (Redundant Array of Inexpensive Drives), they are sold, for the most part, as individual cards due to their complexity. RAID cards contain not only the controller itself, but also a redundancy information calculation acceleration chip (XOR engine), as well as cache memory. A small amount of memory is sometimes soldered onto the card (most often 128 MB), but some cards allow you to expand the amount using a DIMM or SO-DIMM.

When choosing a host adapter or RAID controller, you should clearly define what you need. The range of new devices is growing just before our eyes. Simple multiport host adapters will cost relatively little, while powerful RAID cards will cost a lot. Consider where you will place your drives: external storage requires at least one external slot. Rack servers typically require low profile cards.

If you need RAID, then decide whether you will use hardware acceleration. Some RAID cards take CPU resources for XOR calculations for RAID 5 or 6 arrays; others use their own XOR hardware engine. RAID acceleration is recommended for environments where the server does more than store data, such as databases or web servers.

All of the host adapter cards that we cited in our article support 300 MB/s per SAS port and allow for very flexible implementation of the storage infrastructure. Today, few people will be surprised by external ports, and take into account the support for both SAS and SATA hard drives. All three cards use the PCI-X interface, but PCI Express versions are already in development.

In our article, we paid attention to cards with eight ports, but the number of connected hard drives is not limited to this. With the help of a SAS expander (external), you can connect any storage. As long as a 4-lane connection is sufficient, you can increase the number of hard drives up to 122. Due to the performance cost of calculating the RAID 5 or RAID 6 parity information, typical external RAID storages will not be able to load the quad-lane bandwidth enough, even if a large number of drives are used.

48300 is a SAS host adapter designed for the PCI-X bus. The server market today continues to be dominated by PCI-X, although more and more motherboards are equipped with PCI interfaces express.

The Adaptec SAS 48300 uses a PCI-X interface at 133 MHz, giving a throughput of 1.06 GB/s. Fast enough if the PCI-X bus is not loaded with other devices. If you include a lower speed device in the bus, then all other PCI-X cards will reduce their speed to the same. For this purpose, several PCI-X controllers are sometimes installed on the board.

Adaptec is positioning the SAS 4800 for midrange and low end servers and workstations. The suggested retail price is $360, which is quite reasonable. The Adaptec HostRAID feature is supported, allowing you to upgrade to the simplest RAID arrays. In this case, these are RAID levels 0, 1, and 10. The card supports an external four-channel SFF8470 connection, as well as an internal SFF8484 connector paired with a cable for four SAS devices, that is, we get eight ports in total.

The card fits into a 2U rack server when a low-profile slot cover is installed. The package also includes a CD with a driver, a quick installation guide, and an internal SAS cable through which up to four system drives can be connected to the card.

SAS player LSI Logic sent us a SAS3442X PCI-X host adapter, a direct competitor to the Adaptec SAS 48300. It comes with eight SAS ports that are split between two quad-lane interfaces. The "heart" of the card is the LSI SAS1068 chip. One of the interfaces is intended for internal devices, the second - for external DAS (Direct Attached Storage). The board uses the PCI-X 133 bus interface.

As usual, 300 MB/s interface is supported for SATA and SAS drives. There are 16 LEDs on the controller board. Eight of them - simple LEDs activity, and eight more are designed to report a system malfunction.

The LSI SAS3442X is a low profile card, so it fits easily into any 2U rack server.

Note driver support for Linux, Netware 5.1 and 6, Windows 2000 and Server 2003 (x64), Windows XP (x64) and Solaris up to 2.10. Unlike Adaptec, LSI chose not to add support for any RAID modes.

RAID adapters

SAS RAID4800SAS is Adaptec's solution for more complex SAS environments and can be used for application servers, streaming servers, and more. Before us, again, is an eight-port card, with one external four-lane SAS connection and two internal four-lane interfaces. But if used external connection, then only one four-channel interface remains from the internal ones.

The card is also designed for the PCI-X 133 bus, which provides enough bandwidth for even the most demanding RAID configurations.

As for the RAID modes, the SAS RAID 4800 easily outperforms its "younger brother" here: RAID levels 0, 1, 10, 5, 50 are supported by default if you have enough drives. Unlike the 48300, Adaptec has invested two SAS cables so you can connect eight hard drives to the controller right away. Unlike the 48300, the card requires a full-size PCI-X slot.

If you decide to upgrade your card to Adaptec Advanced Data Protection Suite, you'll be able to upgrade to dual redundant RAID modes (6, 60), as well as a range of enterprise-class features: striped mirror drive (RAID 1E), hot spacing (RAID 5EE), and copyback hot spare. The Adaptec Storage Manager utility has a browser-like interface and can be used to manage all Adaptec adapters.

Adaptec offers drivers for Windows Server 2003 (and x64), Windows 2000 Server, Windows XP (x64), Novell Netware, Red Hat Enterprise Linux 3 and 4, SuSe Linux Enterprise Server 8 and 9 and FreeBSD.

SAS snap-ins

The 335SAS is a four-drive SAS or SATA drive accessory, but must be connected to a SAS controller. Thanks to the 120mm fan, the drives will be well cooled. You will also need to connect two Molex power plugs to the equipment.

Adaptec has included an I2C cable that can be used to control the rig via an appropriate controller. But with SAS drives, this will no longer work. An additional LED cable is designed to signal the activity of the drives, but, again, only for SATA drives. The package also includes an internal SAS cable for four drives, so an external four-channel cable will be enough to connect the drives. If you want to use SATA drives, you will have to use SAS to SATA adapters.

The retail price of $369 is not cheap. But you will get a solid and reliable solution.

SAS storage

SANbloc S50 is a 12-drive enterprise-class solution. You will receive a 2U rackmount enclosure that connects to SAS controllers. This is one of the best examples of scalable SAS solutions. The 12 drives can be either SAS or SATA. Or represent a mixture of both types. The built-in expander can use one or two quad-lane SAS interfaces to connect the S50 to a host adapter or RAID controller. Since we have a clearly professional solution, it is equipped with two power supplies (with redundancy).

If you have already purchased an Adaptec SAS host adapter, you can easily connect it to the S50 and manage drives using the Adaptec Storage Manager. If you install 500 GB SATA hard drives, then we get 6 TB of storage. If we take 300 GB SAS drives, then the capacity will be 3.6 TB. Since the expander is connected to the host controller by two four-lane interfaces, we will get a throughput of 2.4 GB / s, which will be more than enough for an array of any type. If you install 12 drives in a RAID0 array, then the maximum throughput will be only 1.1 GB / s. In the middle of this year, Adaptec promises to release a slightly modified version with two independent SAS I/O blocks.

SANbloc S50 contains the function of automatic monitoring and automatic control of fan speed. Yes, the device is too loud, so we were relieved to return it from the lab after the tests were completed. A drive failure message is sent to the controller via SES-2 (SCSI Enclosure Services) or via the physical I2C interface.

Operating temperatures for actuators are 5-55°C, and for accessories - from 0 to 40°C.

At the start of our tests, we got a peak throughput of just 610 MB/s. By changing the cable between the S50 and the Adaptec host controller, we were still able to reach 760 MB / s. We used seven hard drives to load the system in RAID 0 mode. Increasing the number of hard drives did not lead to an increase in throughput.

Test configuration

System hardware
Processors	2x Intel Xeon (Nocona core) 3.6 GHz, FSB800, 1 MB L2 cache
Platform	Asus NCL-DS (Socket 604) Chipset Intel E7520, BIOS 1005
Memory	Corsair CM72DD512AR-400 (DDR2-400 ECC, reg.) 2x 512 MB, CL3-3-3-10
System hard drive	Western Digital Caviar WD1200JB 120 GB, 7200 rpm, 8 MB cache, UltraATA/100
Drive Controllers	Controller Intel 82801EB UltraATA/100 (ICH5) Promise SATA 300TX4 Driver 1.0.0.33 Adaptec AIC-7902B Ultra320 Driver 3.0 Adaptec 48300 8 port PCI-X SAS Driver 1.1.5472 Adaptec 4800 8 port PCI-X SAS Driver 5.1.0.8360 Firmware 5.1.0.8375 LSI Logic SAS3442X 8 port PCI-X SAS Driver 1.21.05 BIOS 6.01
Vaults	4-bay, hot-swappable indoor rig 2U, 12-HDD SAS/SATA JBOD
Net	Broadcom BCM5721 Gigabit Ethernet
video card	built-in ATi RageXL, 8 MB
Tests
performance measurement	c "t h2benchw 3.6
Measuring I/O performance	IOMeter 2003.05.10 Fileserver Benchmark webserver-benchmark database-benchmark Workstation Benchmark
System software and drivers
OS	Microsoft Windows Server 2003 Enterprise Edition Service Pack 1
Platform driver	Intel Chipset Installation Utility 7.0.0.1025
Graphics driver Workstation script. After examining several new SAS hard drives, three related controllers, and two fixtures, it became clear that SAS was indeed a promising technology. If you refer to the SAS technical documentation, you will understand why. Not only is this a successor to serial SCSI (fast, convenient, and easy to use), but it also offers a great level of scalability and infrastructure growth that makes Ultra320 SCSI solutions look like a stone age. And the compatibility is just great. If you're planning to buy professional SATA hardware for your server, SAS is worth a look. Any SAS controller or accessory is compatible with both SAS and SATA hard drives. Therefore, you can create both a high-performance SAS environment and a capacious SATA environment - or both. Convenient support for external storage is another important advantage of SAS. If the SATA storage uses either proprietary solutions or a single SATA/eSATA link, the SAS storage interface allows for increased bandwidth in groups of four SAS links. As a result, we get the opportunity to increase the bandwidth for the needs of applications, and not rest on 320 MB / s UltraSCSI or 300 MB / s SATA. Moreover, SAS expanders allow you to create a whole hierarchy of SAS devices, so that administrators have more freedom of action. The evolution of SAS devices will not end there. It seems to us that the UltraSCSI interface can be considered obsolete and slowly written off. It is unlikely that the industry will improve it, unless it continues to support existing implementations of UltraSCSI. Still new hard drives, latest models storage and snap-ins, as well as an increase in interface speed to 600 MB / s, and then to 1200 MB / s - all this is intended for SAS. What should be a modern storage infrastructure? With the availability of SAS, the days of UltraSCSI are numbered. The sequential version is a logical step forward and does everything better than its predecessor. The question of choosing between UltraSCSI and SAS becomes obvious. Choosing between SAS or SATA is somewhat more difficult. But if you look into the future, then SAS components will still be better. Indeed, for maximum performance or in terms of scalability, there is no alternative to SAS today.

High-performance server drives for mission-critical tasks are rarely seen by IT publications. No wonder, because we are more focused on the mass buyer than on system administrators and server equipment suppliers. Meanwhile, testing server HDDs is even more important than testing desktop ones, for several reasons. First, due to more high cost drives and higher sensitivity of server tasks to performance. After mass distribution solid state drives differences between desktop disks are no longer important, and in a server, replacing an HDD with an SSD is far from always advisable. The next circumstance follows from the first: HDD for a desktop or home NAS can be chosen according to basic technical characteristics (volume, spindle speed, platter capacity). In the case of a server HDD, much depends on firmware optimization, which manifests itself in a complex load and, accordingly, requires special tests to capture these features. Finally, at large scales, such a parameter as the ratio of performance to power consumption of the drive comes into play.

Over the past few years, choosing enterprise hard drives has definitely become easier. Models with Fiber Channel and SCSI interfaces have ceased to be produced. Drives are divided into two classes: models in the 3.5-inch form factor are limited to a rotation speed of 7200 rpm, have a SAS or SATA interface - to choose from and are designed to store "cold" data (nearline storage). Drives with a speed of 10,000-15,000 rpm use the SAS interface and, for the most part, have moved to the 2.5-inch form factor (SFF - Small Form Factor), which allows you to increase the number of spindles per unit in the rack. Only HGST still has 15K-class drives in 3.5-inch form factor with Fiber Channel ports.

We are already constantly paying attention to nearline drives in a SATA configuration, but the test of SAS / SCSI drives is published for the first time on 3DNews.

⇡ Test participants

The following devices took part in the comparison:

• HGST Ultrastar C10K1800 1.8TB (HUC101818CS4200);
• HGST Ultrastar C15K600 600 GB (HUC156060CSS200);
• Seagate Savvio 10K.6 900 GB (ST900MP0006);
• Seagate Enterprise Performance 10K HDD v7 1.2TB (ST1200MM0017);
• Seagate Enterprise Performance 15K HDD v5 600 GB (ST600MP0035);
• Toshiba AL13SEB 900 GB (AL13SEB900);
• Toshiba AL13SXB 600 GB (AL13SXB600N);
• WD VelociRaptor 1TB (WD1000DHTZ).

Unlike desktop hard drives and NAS hard drives, SAS drives are not so different from each other. All participants:

a) are available in a 2.5-inch form factor with a thickness of 15 mm;

b) have two SAS ports to improve fault tolerance;

c) prepared for 24/7 operation in a telecommunications rack;

d) allow the user to configure the sector size for recording additional metadata;

e) are characterized by the same reliability indicators (MTBF, number of head parking cycles);

e) are sold with a five-year manufacturer's warranty.

For testing, models of the maximum volume in the corresponding lines were selected. The products of all companies that produce HDDs today are presented, with one exception. We have exhausted all the possibilities to get a WD Xe drive for a test (except just to buy it for a lot of money), and recently this brand has completely disappeared from the Western Digital corporate website - apparently, it is being discontinued. As a result, of all drives with a spindle speed of 10-15 thousand rpm, WD has only VelociRaptor - in fact, a derivative of WD Xe, but with a SATA interface. In order for WD to be at least somehow represented in the review, we included the VelociRaptor in the number of participants. Of course, it cannot be considered a 100% replacement for SAS drives, but a lot of servers run on SATA drives, so VelociRaptor can be used. In addition, if you look at the other side, any of the drives for SAS can be used in a workstation with the appropriate HBA (Host Bus Adapter) instead of VelociRaptor, which also justifies the participation of this drive in today's test.

Manufacturer	HGST	HGST	Seagate	Seagate	Seagate	Toshiba	Toshiba	western digital
Series	Ultrastar C10K1800	Ultrastar C15K600	Savvio 10K.6	Enterprise Performance 10K HDD v7	Seagate Enterprise Performance 15K HDD v5	AL13SEB	AL13SXB	VelociRaptor
Model Number	HUC101818CS4200	HUC156060CSS200	ST900MM0006	ST1200MM0017	ST600MP0035	AL13SEB900	AL13SXB600N	WD1000CHTZ/WD1000DHTZ
Form factor	2.5 inches	2.5 inches	2.5 inches	2.5 inches	2.5 inches	2.5 inches	2.5 inches	3.5/2.5 inches
Interface	SAS 12Gb/s	SAS 12Gb/s	SAS 6Gb/s	SAS 6Gb/s	SAS 12Gb/s	SAS 6Gb/s	SAS 6Gb/s	SATA 6Gb/s
dual-port	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Not
Capacity, GB	1 800	600	900	1 200	600	900	600	1000
Configuration
Spindle speed, rpm	10 520	15 030	10 000	10 000	15 000	10 500	15 000	10 000
Data recording density, GB/platter	450	200	300	300	200	240	ND	334
Number of plates/heads	4/8	3/6	3/6	4/8	3/6	4/8	ND	3/6
Buffer size, MB	128	128	64	64	128	64	64	64
Sector size, bytes	4096-4224	512-528	512-528	512-528	4096-4224	512-528	512-528	512
Performance
Max. sustained sequential read speed, MB/s	247	250	195	195	246	195	228	200
Max. sustained sequential write speed, MB/s	247	250	195	195	246	195	228	200
Burst rate, read/write, MB/s	261	267
Internal data transfer rate, MB/s	1307-2859	1762-3197	1440-2350	1440-2350	ND	ND	ND	ND
Average seek time: read/write, ms	3,7/4,4	2,9/3,1	ND	ND	ND	3,7/4,1	2,7/2,95	ND
Track-to-track seek time: read/write, ms	ND	ND	ND	ND	ND	0,2/22	ND	ND
Full stroke seek time: read/write, ms	7,3/7,8	7,3/7,7	ND	ND	ND	ND	ND	ND
Reliability
MTBF (mean time between failures), h	2 000 000	2 000 000	2 000 000	2 000 000	2 000 000	2 000 000	2 000 000	1 400 000
AFR (annualized failure rate), %	ND	0,44	0,44	0,44	0,44	ND	0,44	ND
Number of head parking cycles	600 000	600 000	ND	ND	ND	ND	600 000	600 000
physical characteristics
Power consumption: idle / read-write, W	5,4/7,6	5,8/7,5	3,9/7,8	4,6/8,1	5,3/8,7	3.9/ND	5,0/9,0	4,2/5,8
Typical noise level: idle/searching	34/38 dBA	32/38 dBA	30 dBA / ND	31 dBA / ND	32.5/33.5 dBA	30 dBA / ND	33 dBA / ND	30/37 dBA
Maximum temperature, °C: disk on / disk off	55/70	55/70	60/70	60/70	55/70	55/70	55/70	55/70
Shock resistance: drive enabled (read) / drive disabled		30 g (2 ms) - recording / 300 g (2 ms)	25 g (2 ms) / 400 g (2 ms)	25 g (2 ms) / 400 g (2 ms)	25 g (2 ms) / 400 g (2 ms)	100 g (1 ms) / 400 g (2 ms)	100 g (1 ms) / 400 g (2 ms)	30 g (2 ms) / 300 g (2 ms)
Dimensions: L × H × D, mm	101×70×15	100×70×15	101×70×15	101×70×15	101×70×15	101×70×15	101×70×15	101 x 70 x 15/ 147 x 102 x 26
Weight, g	220	219	212	204	230	240	230	230/500
Warranty period, years	5	5	5	5	5	5	5	5
Average retail price, rub.*	161 000	36 000	20 000	26 900	49 600	17 800	24 100	14 000 / 12 600

⇡ Description of test participants

HGST Ultrastar C10K1800 1.8TB (HUC101818CS4200)

This is the largest drive in HGST's latest 10K lineup. The Ultrastar C10K1800 series is notable in several respects. Models ending in S420x achieve 450 GB per platter thanks to their high recording density using 4K sector formatting (native or 512-byte sector emulation). Therefore, the disk can hold up to 1.8 TB, and the sequential read / write speed has reached the level of the HDD class of 15 thousand rpm.

The rest of the line consists of disks with a markup of 512-528 bytes, with less outstanding speed and up to 1.2 TB.

All models in the C10K1800 line have a so-called media cache. In several places on the surface of the plates, areas serving as a non-volatile cache are highlighted. Instead of carrying data to the requested sector, the write head of the disk flushes it to the nearest cache area, and when the disk is idle, it is moved to the right place.

Incidentally, this is the most expensive disc in the test, fantastically expensive - an average of 161,000 rubles in Moscow online stores. And in America, by the way, it's much cheaper - $800 at newegg.com.

HGST Ultrastar C10K1800 1.8TB (HUC101818CS4200)

HGST Ultrastar C15K600 600 GB (HUC156060CSS200)

The only 15K RPM 2.5" drive line in the HGST range. Ultrastar C15K600 drives simultaneously have the highest sequential read/write speed and low latency at the same time. Physical Formatting plates are performed in sectors of 512-528 or 4096-4224 bytes (with native access or emulation of 512 bytes). The most involved in testing capacious model in the line - 600 GB with sectors of 4 KB.

HGST Ultrastar C15K600 600 GB (HUC156060CSS200)

Seagate Savvio 10K.6 900 GB (ST900MP0006)

These are rather old drives - the generation before last compared to the current Enterprise Performance 10K line from Seagate. Therefore, the performance of the Savvio 10K.6 is no longer class-leading. The plates were formatted in sectors of 512-528 bytes. However, these disks are still on sale, they have a good volume (up to 900 GB) and are relatively inexpensive.

Seagate Savvio 10K.6 900 GB (ST900MP0006)

Seagate Enterprise Performance 10K HDD v7 1.2TB (ST1200MM0017)

This series also formally became obsolete by the time the test was released, giving way to Enterprise Performance 10K HDD v8. These drives differ from Savvio 10K.6 only in increased capacity up to 1.2 TB, but this was achieved by increasing the number of platters, not the recording density, so there is no difference with the previous generation in terms of the declared performance. The model ST1200MM0017 participating in testing has built-in encryption.

Seagate Enterprise Performance 10K HDD 1.2TB (ST1200MM0007)

Seagate Enterprise Performance 15K HDD v5 600 GB (ST600MP0035)

This is the current line of Seagate drives with a spindle speed of 15 thousand rpm. Disks have sector markings of 512-528 or 4096-4224 bytes (natively or with 512 bytes emulation). The maximum capacity (600 GB) drive with 4-kilobyte sectors was tested.

Seagate Enterprise Performance 15K HDD 600 GB (ST600MP0035)

Toshiba AL13SEB 900 GB (AL13SEB900)

According to the main characteristics, this is an analogue of Seagate Savvio 10K.6: 10,000 rpm, volume up to 900 GB, formatting by sectors of 512-528 bytes. Toshiba does not offer drives with built-in encryption in this series.

Toshiba AL13SXB 600 GB (AL13SXB600N)

In this series of 15,000 rpm discs, models with names like AL13SXB**0N are formatted with a sector size of 512-528 bytes. We took the oldest of them for testing. Models with names like AL13SXB**E* use 4K sectors and also support a 12Gb/s SAS interface. There is no built-in encryption in the entire AL13SXB series.

Toshiba 900 GB (AL13SEB900)

WD VelociRaptor 1TB (WD1000CHTZ/WD1000DHTZ)

In terms of physical data, VelociRaptor differs little from its prototype - WD Xe: the same 10,000 rpm and almost the same linear performance. VelociRaptor uses Advanced Format partitioning (4 KB sectors), and the amount available to the user is higher than that of similar WD Xe (1 TB in the case of the older model).

Since this is a SATA drive, functionally it is not a complete analogue of SAS drives. In particular, two-port connectivity, sector size configuration, and built-in encryption can be forgotten. In addition, SAS drives are usually made more reliable, which is noticeable when comparing their claimed MTBF with that of the VelociRaptor. Still, in terms of performance, this drive can be considered as a server ten-thousander for the poor. There are versions of the "lizard" with a radiator-adapter to the form factor 3.5 inches (DHTZ), as well as "naked" versions of 2.5 inches (CHTZ).

WD VelociRaptor 1TB (WD1000DHTZ)

⇡ Testing methodology

Isolated Performance Tests

Performed using Iometer 1.1.0. The volume and speed of data transfer is indicated in binary units (1 KB = 1024 bytes). Block boundaries are aligned with the 4 KB markup.

1. Sequential read/write of 128 KB block data with a request queue depth of 256.
2. Random read / write blocks from 512 bytes to 2 MB with a request queue depth of 256.
3. Mixed read/write of 128 KB blocks with a request queue depth of 256. The share of read and write operations varies from 0 to 100% in 10% increments.
4. Dependence of throughput on the length of the command queue. Reading blocks of 4 KB is performed, the depth of the request queue varies from 1 to 256 in steps of a power of two. A similar test for writing blocks is not carried out, because. hard drives do not differ in this parameter.
5. Steady response time. Random read/write of 512-byte blocks with a request queue depth of 1 is performed. The test continues for 10 minutes.
6. Constancy of response time. Random reading/writing of blocks of 4 KB in size with a request queue depth of 256 is performed. For each segment of the test with a duration of 1 s, the average and maximum values ​​​​of the response time are recorded, on the basis of which: a) the average values ​​of both indicators are calculated; b) standard deviation of the average response time.
7. Multi-threaded read/write. Four threads are created that perform sequential reading/writing of 64 KB blocks with a request queue depth of 1. The threads have access to non-overlapping 100 GB address spaces, which are located close to each other in the disk space, starting from sector zero. The aggregate throughput of all streams is measured, as well as each of them individually.

Simulated Load Tests

Run in Iometer 1.1.0. The volume and speed of data transfer is indicated in binary units (1 KB = 1024 bytes). Block boundaries are aligned with the 4 KB markup. The command queue depth is 256.

Block size	Share of all requests	Share reading	Random access share
Database
8 KB	100%	67%	100%
File Server
512 bytes	10%	80%	100%
1 KB	5%	80%	100%
2 KB	5%	80%	100%
4 KB	60%	80%	100%
8 KB	2%	80%	100%
16 KB	4%	80%	100%
32 KB	4%	80%	100%
64 KB	10%	80%	100%
Work station
8 KB	100%	80%	80%
Web server
512 bytes	22%	100%	100%
1 KB	15%	100%	100%
2 KB	8%	100%	100%
4 KB	23%	100%	100%
8 KB	15%	100%	100%
16 KB	2%	100%	100%
32 KB	6%	100%	100%
64 KB	7%	100%	100%
128 KB	1%	100%	100%
512 KB	1%	100%	100%

test bench

The drives were connected to the LSI SAS 9211-8i adapter, for which we express our gratitude to the Russian representative office of LSI.

⇡ Performance, basic tests

Sequential Read/Write

• Drives with a spindle speed of 15 thousand rpm rule the ball in the sequential read / write test. However, this group has its own leader - Seagate Enterprise Performance 15K HDD v5.
• Ultrastar C10K1800 is not inferior to 15K category drives due to high recording density.
• But the presented ten-thousanders differ little in terms of linear access speed.

Free reading

• 15-thousanders and in this discipline dominate over their low-speed counterparts.
• The spread of indicators within HDD categories with the same spindle speed is small. We can single out only the HGST Ultrastar C15K600 as the formal leader in its group and the VelociRaptor, which is clearly inferior to its counterparts.

Arbitrary entry

The results of the random write test turned out to be less predictable than in the previous test, since they are determined not only by the mechanics of the HDD, but also by the nature of the buffer usage.

• The HGST Ultrastar C15K600 demonstrated tremendous performance, completely unattainable for competing devices.
• The two remaining 15K drives also have a big advantage over HDDs with lower spindle speeds.
• The 10Ks themselves make up a homogeneous group, with the exception of the Ultrastar C10K1800. It goes far beyond its class and is second only to the C15K600 drive from the same manufacturer. Here it is, the vaunted media cache, in action!

Steady response time

• Although the load continues for 10 minutes, it may not completely fill the buffer on some drives, so the results for writing data do not reflect what this test is aimed at - the latency of the drive mechanics.
• On the contrary, when reading with a queue length of one instruction, the buffer is not a helper. As a result, the rivals lined up in accordance with the speed of rotation of the spindle (the higher it is, the faster the response time). No significant difference was found between devices of the same category.

⇡ Performance, advanced analysis

Mixed Read/Write

• The 15K drives are still on top, with the exception of the Ultrastar C15K600, which sank especially hard under mixed loads.
• Ultrastar C10K1800 has once again stood out among its peers. Of the other ten-thousanders, we note Toshiba AL13SEB. They are all about the same at 100 percent read or write, but the AL13SEB retains the best performance under mixed workloads.

Dependence of throughput on the length of the command queue

• All drives are able to benefit from a long queue of commands and reach peak throughput at 64 commands. Only the VelociRaptor is content with a queue of 32 teams.

Multi-threaded reading

• Most of the participants in the test evenly distribute resources among the four threads. Which, however, leads to low overall productivity.
• Toshiba AL13SEB and WD VelociRaptor, on the contrary, sacrifice one of the threads during multi-threaded reading, thereby increasing the data transfer rate in the others and the overall throughput.

Multi-threaded recording

• When writing to four streams, none of the disks is cunning: performance is evenly distributed between all streams.
• As you can see, not so much depends on the mechanics of the disk in this test. The 15K models from Seagate and Toshiba took first place, but the Ultrastar 15K600 is an obvious outsider.

Response time consistency

• When reading data, all drives are characterized by a significant difference between the average and maximum response times. Only the VelociRaptor stands out with a better average to maximum response time ratio.
• When recording, the peak values ​​of the response time are smoothed by the buffer and differ little from the average.

• Test participants differ most in terms of write access time spread. The Ultrastar C10K1800 has the most consistent performance. Toshiba AL13SEB900, on the other hand, has a much higher standard deviation of access time.

Among server ten-thousanders, disks do not differ so much from each other, but formally, Seagate Savvio 10K.6 achieved the best results. VelociRaptor, on the other hand, always trails behind.

Most ten-thousanders are similar in their main aspects, but it is worth highlighting the HGST Ultrastar C10K1800 (HUC101818CS4200), which is inferior to more resourceful colleagues of the 15K class only in random read speed and at the same time has a record volume of 1.8 TB. However, these advantages did not affect the results of tests with emulated applications.

Seagate Savvio 10K.6 900 GB (ST900MP0006) and Seagate Enterprise Performance 10K HDD v7 1.2 TB (ST1200MM0007) deliver consistently high performance without surprises. Toshiba AL13SEB900 coped with the tests a little worse than other ten-thousanders.

The WD VelociRaptor 1TB (WD1000DHTZ) can be considered a "poor man's" high-performance HDD if the SAS protocol is not a mandatory item in the terms of reference. According to its characteristics, this is a typical 10K class disk, only in comparison with true server drives, the random read speed leaves much to be desired, which also manifested itself in "emulators".

Hard drive for the server, features of choice

The hard drive is the most valuable component in any computer. After all, it stores information with which the computer and the user work, in the event that we are talking about personal computer. Every time a person sits down at a computer, he expects that the operating system loading screen will now run through, and he will start working with his data, which the hard drive will give out “to the mountain” from his bowels. If we are talking about a hard drive, or even an array of them as part of a server, then there are tens, hundreds and thousands of such users who expect to get access to personal or work data. And all their quiet work or recreation and entertainment depends on these devices that constantly store data in themselves. Already from this comparison it is clear that requests for hard drives of home and industrial class are not equivalent - in the first case, one user works with it, in the second - thousands. It turns out that the second hard drive should be more reliable, faster, more stable than the first one many times over, because they work with it, many users rely on it. This article will discuss the types of hard drives used in the corporate sector and their design features to achieve the highest reliability and performance.

SAS and SATA drives - so similar and so different

Until recently, the standards of industrial and consumer hard drives differed significantly and were incompatible - SCSI and IDE, now the situation has changed - the vast majority of hard drives on the market are SATA and SAS (Serial Attached SCSI) hard drives. The SAS connector is versatile and form factor compatible with SATA. This allows you to directly connect to the SAS system both high-speed, but at the same time small capacity (up to 300 GB at the time of writing) SAS drives, as well as slower, but many times more capacious SATA drives (up to 2 TB at the time of writing). ). Thus, in one disk subsystem, it is possible to combine vital applications that require high performance and rapid data access, and more economical applications with a lower cost per gigabyte.

This interoperability benefits both backplate manufacturers and end users by reducing hardware and engineering costs.

That is, both SAS devices and SATA devices can be connected to SAS connectors, and only SATA devices can be connected to SATA connectors.

SAS and SATA - high speed and large capacity. What to choose?

SAS disks, which replaced SCSI disks, completely inherited their main properties that characterize a hard drive: spindle speed (15000 rpm) and volume standards (36,74,147 and 300 GB). However, the SAS technology itself differs significantly from SCSI. Let's take a quick look at the main differences and features: The SAS interface uses a point-to-point connection - each device is connected to the controller by a dedicated channel, unlike it, SCSI works on a common bus.

SAS supports a large number of devices (> 16384), while the SCSI interface supports 8, 16, or 32 devices on the bus.

The SAS interface supports data transfer rates between devices at speeds of 1.5; 3; 6 Gb / s, while the SCSI interface bus speed is not allocated to each device, but is divided between them.

SAS supports the connection of slower SATA devices.

SAS configurations are much easier to assemble and install. Such a system is easier to scale. In addition, SAS hard drives inherited the reliability of SCSI hard drives.

When choosing a disk subsystem - SAS or SATA, you need to be guided by what functions will be performed by the server or workstation. To do this, you need to decide on the following questions:

1. How many simultaneous, diverse requests will the disk process? If large - your clear choice - SAS disks. Also, if your system will serve a large number of users - choose SAS.

2. How much information will be stored on the disk subsystem of your server or workstation? If more than 1-1.5 TB, you should pay attention to a system based on SATA hard drives.

3. What is the budget allocated for the purchase of a server or workstation? It should be remembered that in addition to SAS disks, you will need a SAS controller, which also needs to be taken into account.

4. Do you plan, as a result, to increase the volume of data, increase productivity or increase the fault tolerance of the system? If so, then you need a SAS-based disk subsystem, it is easier to scale and more reliable.

5. Your server will run mission-critical data and applications - your choice is heavy-duty SAS drives.

A reliable disk subsystem, it is not only high-quality hard disks from a well-known manufacturer, but also an external disk controller. They will be discussed in one of the following articles. Consider SATA drives, what types of these drives are and which ones should be used when building server systems.

SATA drives: consumer and industrial sector

SATA drives used everywhere, from consumer electronics and home computers to high-performance workstations and servers, differ in subspecies, there are drives for use in household appliances, with low heat dissipation, power consumption, and as a result, low performance, there are drives - middle class, for home computers, and there are drives for high-performance systems. In this article, we will consider the class of hard drives for productive systems and servers.

Performance characteristics

	Server class HDD	HDD desktop class
Rotational speed	7,200 rpm (nominal)	7,200 rpm (nominal)
Cache size
Average delay time	4.20 ms (nominal)	6.35 ms (nominal)
Transfer rate
Reading from drive cache (Serial ATA)	maximum 3 Gb/s	maximum 3 Gb/s
physical characteristics
Capacity after formatting	1,000,204 MB	1,000,204 MB
Capacity
Interface	SATA 3Gb/s	SATA 3Gb/s
Number of sectors available to the user	1 953 525 168	1 953 525 168
Dimensions
Height	25.4mm	25.4mm
Length	147 mm	147 mm
Width	101.6 mm	101.6 mm
	0.69 kg	0.69 kg
impact resistance
Shock resistance in working condition	65G, 2ms	30G; 2 ms
Shock resistance when not in use	250G, 2ms	250G, 2ms
Temperature
In working order	-0° C to 60° C	-0° C to 50° C
Out of Service	-40° C to 70° C	-40° C to 70° C
Humidity
In working order		relative humidity 5-95%
Out of Service	relative humidity 5-95%	relative humidity 5-95%
Vibration
In working order
Linear	20-300Hz, 0.75g (0 to peak)	22-330Hz, 0.75g (0 to peak)
Free	0.004 g/Hz (10 - 300 Hz)	0.005 g/Hz (10 - 300 Hz)
Out of Service
low frequency	0.05 g/Hz (10 - 300 Hz)	0.05 g/Hz (10 - 300 Hz)
High frequency		20-500Hz, 4.0G (0 to peak)

The table shows the characteristics of hard drives from one of the leading manufacturers, in one column data are given for a server-class SATA hard drive, in the other for a regular SATA hard drive.

From the table we can see that disks differ not only in performance characteristics, but also in operational characteristics, which directly affect the life expectancy and successful operation of the hard drive. You should pay attention to the fact that outwardly these hard drives differ insignificantly. Consider what technologies and features allow you to do this:

Reinforced shaft (spindle) hard drive, for some manufacturers, is fixed at both ends, which reduces the influence of external vibration and helps to accurately position the head unit during read and write operations.

The use of special intelligent technologies that take into account both linear and angular vibration, which reduces the positioning time of the heads and increases the performance of disks up to 60%

RAID runtime debugging feature - prevents hard drives from dropping out of RAID, which is a characteristic feature of conventional hard drives.

The height adjustment of the heads in combination with the technology of preventing contact with the surface of the plates, which leads to a significant increase in the life of the disk.

A wide range of self-diagnostic functions that allow you to predict in advance the moment when the hard drive will fail and warn the user about it, which allows you to have time to save information to a backup drive.

Features that reduce the rate of unrecoverable read errors, which increases the reliability of the server hard drive compared to conventional hard drives.

Speaking about the practical side of the issue, we can confidently say that specialized hard drives in servers "behave" much better. AT technical service there are many times fewer calls for the instability of RAID arrays and hard drive failures. Support by the manufacturer of the server segment of hard drives is much faster than conventional hard drives, due to the fact that the industrial sector is a priority for any manufacturer of data storage systems. After all, it is in it that the most advanced technologies that guard your information are used.

Analogue of SAS disks:

Hard drives from Western Digital VelociRaptor. These 10K RPM drives are equipped with a SATA 6 Gb/s interface and 64 MB of cache. The MTBF of these drives is 1.4 million hours.
More details on the manufacturer's website www.wd.com

You can order an assembly of a server based on SAS or an analogue of SAS hard drives in our Status company in St. Petersburg, you can also buy or order SAS hard drives in St. Petersburg:

• call +7-812-385-55-66 in St. Petersburg
• write to the address
• Leave an application on our website on the page "Online application"

#SAS

SAS (Serial Attached SCSI)- a serial computer interface designed to connect various storage devices, such as tape drives. SAS is designed to replace the parallel SCSI interface and uses the same SCSI command set.

SAS is backwards compatible with SATA: SATA II and SATA 6 Gb/s devices can be connected to a SAS controller, but SAS devices cannot be connected to a SATA controller. The latest implementation of SAS provides data transfer at speeds up to 12 Gb / s per line. 24Gb/s SAS specification expected by 2017

SAS combines the advantages of SCSI interfaces (deep sorting of the command queue, good scalability, high noise immunity, long maximum cable lengths) and Serial ATA (thin, flexible, cheap cables, hot-pluggability, point-to-point topology that allows you to achieve better performance in complex configurations) with new unique features - such as an advanced connection topology using hubs called SAS expanders (SAS expanders), connecting two SAS channels to one (both to increase reliability and performance), work on one disk as with SAS and SATA interface.

Combined with the new addressing system, this allows you to connect up to 128 devices per port and have up to 16256 devices on the controller, without the need for any jumper manipulation, etc. Removed the 2 Terabyte limit on LUN space.

The maximum cable length between two SAS devices is 10 m when using passive copper cables.

Actually, the SAS data transfer protocol means three protocols at once - SSP (Serial SCSI Protocol), which provides the transfer of SCSI commands, SMP (SCSI Management Protocol), which works with control SCSI commands and is responsible, for example, for interacting with SAS expanders, and STP (SATA Tunneled Protocol), which implements support for SATA devices.

Currently manufactured ones have internal connectors like SFF-8643 (it can also be called mini SAS HD), but you can still meet connectors like SFF-8087 (mini SAS), which has 4 SAS channels.

The external interface option uses the SFF-8644 connector, but the SFF-8088 connector may still be found. It also supports four SAS channels.

SAS controllers are fully compatible with SATA drives and SATA cages/backplanes– the connection is usually made with cables: . The cable looks like this:

SFF-8643 -> 4 x SAS/SATA

Usually SAS cages / backplanes have SATA connectors on the outside and you can always insert regular SATA drives into them, so they (such cages) are usually called SAS / SATA.

However, there are reverse versions of such a cable for connecting a backplane with internal SFF-8087 connectors to a SAS controller that has regular SATA connectors. These cables are not interchangeable with each other.

SAS drives cannot be connected to a SATA controller or installed in a SATA cage/backplane.

To connect SAS disks to a controller with internal SFF-8643 or SFF-8087 connectors without using SAS cages, you must use a cable like SFF-8643->SFF-8482 or SFF-8087->SFF-8482, respectively.

Existing versions of the SAS interface (1.0, 2.0, and 3.0) are compatible with each other, that is, a SAS2.0 drive can be connected to a SAS 3.0 controller and vice versa. In addition, the future version of 24 Gb / s will also be backwards compatible.

Types of SAS Connectors

Image

code name

Also known as

External/ interior

Number of contacts

Number of devices

For over 20 years, the parallel bus interface has been the most common communication protocol for most digital storage systems. But as the need for bandwidth and system flexibility has grown, the shortcomings of the two most common parallel interface technologies, SCSI and ATA, have become apparent. The lack of compatibility between SCSI and ATA parallel interfaces - different connectors, cables, and instruction sets used - increases the cost of system maintenance, research and development, education, and qualification of new products.

To date, parallel technologies still suit users of modern enterprise systems in terms of performance, but the growing need for higher speeds, higher data transfer integrity, reduced physical size, and wider standardization casts doubt on the ability of a parallel interface without unnecessary costs to keep up with rapidly growing CPU performance and hard drive speeds. In addition, in the face of austerity, it is becoming increasingly difficult for enterprises to find funds to develop and maintain heterogeneous back panel connectors of server cases and external disk arrays, verify heterogeneous interface compatibility, and inventory heterogeneous I/O connections.

The use of parallel interfaces also comes with a number of other problems. Parallel data transmission over a wide stub cable is subject to crosstalk, which can create additional noise and signal errors - to avoid this trap, you have to reduce the signal speed or limit the length of the cable, or both. Termination of parallel signals is also associated with certain difficulties - you have to terminate each line separately, usually the last drive performs this operation in order to prevent signal reflection at the end of the cable. Finally, the large cables and connectors used in parallel interfaces make these technologies unsuitable for new compact computing systems.

Introducing SAS and SATA

Serial technologies such as Serial ATA (SATA) and Serial Attached SCSI (SAS) overcome the architectural limitations of traditional parallel interfaces. These new technologies got their name from the method of signal transmission, when all information is transmitted sequentially (English serial), in a single stream, in contrast to multiple streams that are used in parallel technologies. The main advantage of the serial interface is that when data is transferred in a single stream, it moves much faster than when using a parallel interface.

Serial technologies combine many bits of data into packets and then transfer them over a cable at speeds up to 30 times faster than parallel interfaces.

SATA expands on the capabilities of traditional ATA technology by enabling data transfer between disk drives at rates of 1.5 GB per second or more. Due to its low cost per gigabyte of disk capacity, SATA will continue to be the dominant disk interface in desktop PCs, entry-level servers, and network storage systems, where cost is one of the main considerations.

SAS, the successor to parallel SCSI, builds on the proven high functionality of its predecessor and promises to greatly expand the capabilities of today's enterprise storage systems. SAS has a number of advantages that are not available with traditional storage solutions. In particular, SAS allows up to 16,256 devices to be connected to a single port and provides a reliable point-to-point serial connection at speeds up to 3 Gb / s.

In addition, the smaller SAS connector provides full two-port connectivity for both 3.5" and 2.5" hard drives (previously only available on 3.5" Fiber Channel hard drives). This is a very useful feature when you need to fit a lot of redundant drives into a compact system such as a low profile blade server.

SAS improves drive addressing and connectivity with hardware expanders that allow a large number of drives to be connected to one or more host controllers. Each expander provides connections for up to 128 physical devices, which can be other host controllers, other SAS expanders or disk drives. This scheme scales well and allows you to create enterprise-scale topologies that easily support multi-node clustering for automatic system recovery in case of failure and for load balancing.

One of the biggest benefits of the new serial technology is that the SAS interface will also be compatible with more cost-effective SATA drives, allowing system designers to use both types of drives in the same system without the additional expense of supporting two different interfaces. Thus, the SAS interface, representing the next generation of SCSI technology, allows you to overcome existing restrictions parallel technologies in terms of performance, scalability and data availability.

Multiple levels of compatibility

Physical Compatibility

The SAS connector is universal and form factor compatible with SATA. This allows both SAS and SATA drives to be directly connected to the SAS system, thus enabling the system to be used either for mission-critical applications that require high performance and fast data access, or for more cost-effective applications with a lower cost per gigabyte.

The SATA command set is a subset of the SAS command set, which provides compatibility between SATA devices and SAS controllers. However, SAS drives cannot work with SATA controller, so they are equipped with special keys on the connectors to eliminate the possibility of incorrect connection.

In addition, the similar physical dimensions of the SAS and SATA interfaces allow for a new universal SAS backplate that allows both SAS and SATA drives to be connected. As a result, there is no need to use two different backplates for SCSI and ATA drives. This interoperability benefits both backplate manufacturers and end users by reducing hardware and engineering costs.

Protocol level compatibility

SAS technology includes three types of protocols, each of which is used to transfer different types of data over a serial interface, depending on which device is being accessed. The first is the serial SCSI protocol (Serial SCSI Protocol SSP), which transmits SCSI commands, the second is the SCSI Management Protocol (SMP), which transmits control information to the expanders. The third, SATA Tunneled Protocol STP, establishes a connection that allows SATA commands to be sent. Using these three protocols, the SAS interface is fully compatible with existing SCSI applications, management software, and SATA devices.

This multi-protocol architecture, combined with the physical compatibility of SAS and SATA connectors, makes SAS technology the universal link between SAS and SATA devices.

Compatibility Benefits

Compatibility between SAS and SATA brings a number of benefits to system designers, builders, and end users.

With SAS and SATA compatibility, system designers can use the same backplates, connectors, and cable connections. Upgrading the system from SATA to SAS is actually a replacement of disk drives. In contrast, for users of traditional parallel interfaces, moving from ATA to SCSI means changing back panels, connectors, cables, and drives. Other cost-effective interoperability benefits of serial technologies include simplified certification and asset management.

VAR resellers and system builders can quickly and easily reconfigure custom systems by simply installing the appropriate disk drive into the system. There is no need to work with incompatible technologies and use special connectors and different cable connections. What's more, the added flexibility to choose the best price/performance ratio will allow VAR resellers and system builders to better differentiate their products.

For end users, SATA and SAS compatibility means a new level of flexibility when it comes to choosing the best price/performance ratio. SATA drives are the best solution for low-cost servers and storage systems, while SAS drives provide maximum performance, reliability and management software compatibility. The ability to upgrade from SATA to SAS drives without having to purchase a new system greatly simplifies the purchasing decision, protects system investment, and lowers total cost of ownership.

Joint development of SAS and SATA protocols

On January 20, 2003, the SCSI Trade Association (STA) and the Serial ATA (SATA) II Working Group announced a collaboration to ensure that SAS technology is compatible with SATA disk drives at the system level.

The collaboration of the two organizations, as well as the joint efforts of storage vendors and standards committees, is aimed at developing even more precise compatibility guidelines that will help system designers, IT professionals and end users fine-tune their systems to achieve optimal performance. and reliability and lower total cost of ownership.

The SATA 1.0 specification was approved in 2001, and SATA products from various manufacturers are on the market today. The SAS 1.0 specification was approved in early 2003, and the first products should hit the market in the first half of 2004.