Comparison of SCSI, SAS and SATA interfaces. What is the difference between SATA, SAS and SSD drives Connections and interfaces

In modern computer systems ah, SATA and SAS interfaces are used to connect the main hard drives. As a rule, the first option suits home workstations, the second - server ones, so the technologies do not compete with each other, meeting different requirements. The significant difference in cost and memory size makes users wonder how SAS differs from SATA and look for compromises. Let's see if this makes sense.

SAS(Serial Attached SCSI) is a serial interface for connecting storage devices, developed on the basis of parallel SCSI to execute the same set of commands. Used primarily in server systems.

SATA(Serial ATA) is a serial data exchange interface based on parallel PATA (IDE). It is used in home, office, multimedia PCs and laptops.

If we talk about the HDD, then, despite the differing specifications and connectors, there are no cardinal differences between the devices. Backward one-way compatibility allows you to connect to server board disks and on one, and on the second interface.

It is worth noting that both connection options are also real for SSDs, but the significant difference between SAS and SATA in this case will be in the cost of the drive: the first can be dozens of times more expensive with a comparable volume. Therefore, today such a solution, if not rare, is sufficiently balanced, and is intended for fast corporate-level data centers.

Comparison

As we already know, SAS is used in servers, SATA - in home systems. In practice, this means that many users access the former at the same time and solve many tasks, while the latter is dealt with by one person. Accordingly, the server load is much higher, so the disks must be sufficiently fault-tolerant and fast. The SCSI protocols (SSP, SMP, STP) implemented in SAS allow you to process more I / O operations at the same time.

Directly for HDD, the speed of access is determined primarily by the speed of rotation of the spindle. For desktop systems and laptops, 5400 - 7200 RPM is necessary and sufficient. Accordingly, it is almost impossible to find a SATA drive with 10,000 RPM (except to look at the WD VelociRaptor series, again designed for workstations), and anything higher is absolutely unattainable. SAS HDD spins at least 7200 RPM, 10000 RPM can be considered the standard, and 15000 RPM is a sufficient maximum.

Serial SCSI drives are considered to be more reliable and have higher MTBF. In practice, stability is achieved more due to the checksum verification function. SATA drives, on the other hand, suffer from “silent errors”, when data is partially written or corrupted, which leads to bad sectors.

The main advantage of SAS also works for the fault tolerance of the system - two duplex ports that allow you to connect one device via two channels. In this case, information exchange will be carried out simultaneously in both directions, and reliability is ensured by Multipath I / O technology (two controllers insure each other and share the load). The queue of tagged commands is built up to a depth of 256. Most SATA drives have one half-duplex port, and the queue depth using NCQ technology is no more than 32.

The SAS interface assumes the use of cables up to 10 m long. Up to 255 devices can be connected to one port through expanders. SATA is limited to 1m (2m for eSATA), and only supports point-to-point connection of one device.

Prospects for further development - what is the difference between SAS and SATA is also felt quite sharply. The bandwidth of the SAS interface reaches 12 Gb / s, and manufacturers announce support for data transfer rates of 24 Gb / s. The latest revision of SATA stopped at 6 Gb / s and will not evolve in this regard.

SATA drives in terms of the cost of 1 GB have a very attractive price tag. In systems where the speed of access to data is not critical, and the amount of stored information is large, it is advisable to use them.

Table

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 command sets used - increases the cost of system maintenance, research and development, training and qualification of new products.

To date, parallel technologies are still satisfactory for users of modern corporate systems in terms of performance, but growing demands for higher speeds, better data transfer integrity, smaller physical sizes, and more standardization are calling into question the parallel interface's ability to cost-effectively keep pace with rapidly growing CPU performance and drive speed. hard drives. In addition, in an environment of austerity, it is becoming increasingly difficult for enterprises to find funds to develop and maintain heterogeneous back panel connectors for 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 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 systems information storage, 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 cost of supporting two different interfaces. Thus, the SAS interface, representing the next generation of SCSI technology, allows you to overcome existing limitations parallel technologies in terms of performance, scalability and data availability.

Multiple levels of compatibility

The SAS connector is universal and form factor compatible with SATA. This allows both SAS and SATA drives to be directly connected to a 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 a SATA controller, so they are provided with special keys on the connectors to eliminate the possibility of incorrect connection.

In addition, the similar physical parameters of the SAS and SATA interfaces allow for a new universal SAS backplane that supports both SAS and SATA drives. 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 data different types via 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 the transmission of SATA commands. 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.

System designers can use the same backplates, connectors, and cable connections due to SAS and SATA compatibility. 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 in choosing 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. Upgradable from SATA drives to SAS drives without having to purchase new system greatly simplifies the purchasing decision process, protects system investment and reduces total cost of ownership.

Joint development of SAS and SATA protocols

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 to fine-tune their systems even more 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.

In this article, we'll look into the future of SCSI and look at some of the advantages and disadvantages of SCSI, SAS, and SATA interfaces.

In fact, the issue is a bit more complex than just replacing SCSI with SATA and SAS. Traditional parallel SCSI is a tried and tested interface that has been around for a long time. Currently, SCSI offers a very fast data transfer rate of 320 Megabytes per second (Mbps) using the modern Ultra320 SCSI interface. In addition, SCSI offers a wide range of features, including Command-Tag Queuing (a method of optimizing I/O commands to increase performance). SCSI hard drives are reliable; in a short distance, you can create a daisy chain of 15 devices connected to a SCSI link. These features make SCSI an excellent choice for high performance desktops and workstations, up to and including enterprise servers, to this day.

SAS hard drives use the SCSI command set and have the same reliability and performance as SCSI drives, but use a serial version of the SCSI interface at 300 Mbps. Although slightly slower than 320 Mbps SCSI, the SAS interface is capable of supporting up to 128 devices over longer distances than the Ultra320 and can expand to 16,000 devices per channel. SAS hard drives offer the same reliability and rotation speeds (10000-15000) as SCSI drives.

SATA drives are a little different. Where SCSI and SAS drives focus on performance and reliability, SATA drives trade them off in favor of massive capacity increases and cost reductions. For example, a SATA drive in currently reached a capacity of 1 terabyte (TB). SATA is used where maximum capacity is needed, for example, for Reserve copy data or archiving. SATA now offers point-to-point connections at speeds up to 300 Mbps, and easily outperforms the traditional parallel ATA interface at 150 Mbps.

So what will happen to SCSI? It works great. The problem with traditional SCSI is that it's just coming to the end of its useful life. Parallel SCSI at 320 Mb/s will not run much faster on current SCSI cable lengths. In comparison, SATA drives will reach 600 Mb/s in the near future, SAS have plans to reach 1200 Mb/s. SATA drives can also work with the SAS interface, so these drives can be used simultaneously in some storage systems. The potential for increased scalability and data transfer performance far exceeds that of SCSI. But SCSI isn't going away anytime soon. We will see SCSI in small and medium servers for a few more years. As hardware upgrades, SCSI will be systematically replaced by SAS/SATA drives to get faster and more convenient connections.

What is SAS, background It's time to face the obvious: the SCSI standard, even in the most modern implementations like Ultra320 SCSI, has exhausted its capabilities. At the very least, further scaling of its performance, if theoretically possible, will be very expensive. The situation with this highly respected standard looks especially depressing against the backdrop of the rapid development of the entire computer technology and architectures and topologies of storage systems in particular.

Two key factors pushing manufacturers to improve hard drive interfaces are the growing performance of data storage systems with a large number of serviced transactions and the speed of retrieving data from large libraries. Of course, "a holy place is never empty", and the appearance of interfaces like optical FCAL or serial SATA to some extent made it possible to get rid of "bottlenecks" and diversify the list of storage system architectures. However, users accustomed to the possibilities of SCSI still remain fans of this standard. Moreover, a lot of money has been invested in its development.

These are the prerequisites for the birth of a new industrial standard, called serial-attached SCSI - Wikiwand Serial-Attached SCSI, or simply SAS.


To be fair, it should be noted that new standard did not appear suddenly and immediately: the official announcement of SAS technology, which took place on January 28, 2004, was preceded by serious work by a team of developers from different companies and industrial groups - SCSI Trade Association (STA) and International Committee for Information Technology Standards (INCITS), under the auspices of American National Standards Institute (ANSI). The new standard was first talked about in December 2001, when the board of directors of the SCSI Trade Association (STA) voted to define Serial Attached SCSI specifications. Further, on May 2, 2002, the development of the standard was transferred to the T10 committee at INCITS (InterNational Committee for Information Technology Standards), created specifically to support, develop and promote SAS, and the first draft SAS specifications were published in mid-2003.

So, the most important thing to rely on when trying to formulate a definition of the SAS standard: Serial-Attached SCSI is a logical and natural serial extension of the SCSI parallel interface technology used to connect peripherals to computers.
From this, for starters, and push off.

Purpose of the SAS

SAS Connector and Cable Specifications

SAS system topology

Illustration for the principle of organizing a SAS domain
maximum capacity

SAS Protocols

SAS architecture

Conclusion

Adaptec website resources
Maxtor website resources
Seagate website resources

Serial Attached SCSI -
SCSI Architecture Model-3 (SAM-3)
SCSI Primary Commands-3 (SPC-3)
SCSI Block Commands-2 (SBC-2)
SCSI Stream Commands-2 (SSC-2)
SCSI Enclosure Services-2 (SES-2)

SFF 8482 (internal backplane/drive)
SFF 8470 (external 4-wide)
SFF 8223, 8224, 8225 (2.5", 3.5", 5.25" form factors)
SFF 8484 (internal 4-wide)

Serial ATA II: Extensions to Serial ATA 1.0
Serial ATA II: Port Multiplier
Serial ATA II: Port Selector
Serial ATA II: Cables and Connectors Volume 1

International Committee for Information Technology Standards
T11 (Fiber Channel standards)
SCSI Trade Association
SNIA (Storage Networking Industry Association)

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 use and big 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. Since the bus IDs 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 speeds, connectors, and signal voltages (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 (status: 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 next-generation network environments.

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 the new standard SATA II, although during standardization 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). Each Edge expander is allowed up to 128 physical connections, 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 to 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 rackmount 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 not well suited to the requirements of online applications such as 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 either: today the maximum for them 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 power 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 the energy than 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're looking for 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 up resources CPU 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 Express interfaces.

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 an external connection is used, then only one four-channel interface remains from the internal ones.

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

As far as RAID modes are concerned, the SAS RAID 4800 easily outperforms its "younger brother": 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 double 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 provides 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. We have one of best examples 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 automatic monitoring And automatic control 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