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, training, 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 an austerity environment, it is becoming increasingly difficult for enterprises to find funds to develop and maintain heterogeneous back panel connectors for server chassis 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 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, overcomes the existing limitations of 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 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 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 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 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.

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 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 will become 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

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.

Little has changed over the past two years:

• Supermicro is ditching the proprietary "flipped" UIO form factor for controllers. Details will be below.
• LSI 2108 (SAS2 RAID with 512MB cache) and LSI 2008 (SAS2 HBA with optional RAID support) are still in service. Products based on these chips, both from LSI and from OEM partners, are well debugged and are still relevant.
• There were LSI 2208 (the same SAS2 RAID with LSI MegaRAID stack, only with a dual-core processor and 1024MB of cache) and (an improved version of LSI 2008 with a faster processor and PCI-E 3.0 support).

Transition from UIO to WIO

WIO riser RSC-R2UW-4E8

• WIO risers cannot be installed in UIO motherboards (eg X8DTU-F).
• UIO risers cannot be installed in new WIO boards.
• There are risers for WIO (on the motherboard) that have a UIO slot for cards. In case you still have UIO controllers. They are used in platforms under Socket B2 (6027B-URF, 1027B-URF, 6017B-URF).
• New controllers in the UIO form factor will not appear. For example, the USAS2LP-H8iR controller on the LSI 2108 chip will be the last one, there will be no LSI 2208 for UIO - only a regular MD2 with PCI-E x8.

PCI-E controllers

Onboard controllers

• The LSI 2208-based controller soldered on motherboards has a maximum limit of 16 disks. If you add 17, it will simply not be detected, and you will see the message "PD is not supported" in the MSM log. This is offset by a significantly lower price. For example, a bundle "X9DRHi-F + external controller LSI 9271-8i" will cost about $500 more than an X9DRH-7F with LSI 2008 onboard. Bypassing this limitation by flashing in LSI 9271 will not work - flashing another SBR block, as in the case of LSI 2108, does not help.
• Another feature is the lack of support for CacheVault modules, there is simply not enough space on the boards for a special connector, so only BBU09 is supported. The ability to install the BBU09 depends on the enclosure used. For example, the LSI 2208 is used in the 7127R-S6 blade servers, there is a BBU connector, but to mount the module itself, you need an additional MCP-640-00068-0N Battery Holder Bracket.
• The SAS HBA (LSI 2308) firmware will now be required, since in DOS on any of the boards with LSI 2308 sas2flash.exe does not start with the error "Failed to initialize PAL".

Controllers in Twin and FatTwin platforms

• 2027TR-HTRF+ - Chipset SATA
• 2027TR-H70RF+ - LSI 2008
• 2027TR-H71RF+ - LSI 2108
• 2027TR-H72RF+ - LSI 2208

BPN-ADP-S2208L-H6iR (LSI 2208)

Supermicro xxxBE16/xxxBE26 Enclosures

Today's file server or web server is indispensable without a RAID array. Only this mode of operation can provide the required bandwidth and speed of work with the storage system. Until recently, the only hard drives suitable for such work were SCSI drives with a spindle speed of 10-15 thousand revolutions per minute. These drives required a separate SCSI controller to operate. The SCSI data transfer rate reached 320 Mb / s, but the SCSI interface is a regular parallel interface, with all its shortcomings.

More recently, a new disk interface. It was called SAS (Serial Attached SCSI). Recreation centers in Chelyabinsk - Today, many companies already have controllers for this interface in their product line that support all levels of RAID arrays. In our mini-review, we'll take a look at two members of Adaptec's new SAS controller family. These are the 8 port model ASR-4800SAS and the 4+4 port model ASR-48300 12C.

Introduction to SAS

What kind of interface is this - SAS? Actually SAS is a hybrid of SATA and SCSI. The technology has absorbed the advantages of two interfaces. Let's start with the fact that SATA is a serial interface with two independent read and write channels, and each SATA device is connected to a separate channel. SCSI has a very efficient and reliable enterprise data transfer protocol, but the downside is the parallel interface and shared bus for multiple devices. Thus, SAS is free from the disadvantages of SCSI, has the advantages of SATA and provides speeds up to 300 Mb / s per channel. According to the diagram below, you can roughly imagine the connection scheme for SCSI and SAS.

The bidirectionality of the interface reduces latency to zero, since there is no channel switching to read / write.

An interesting and positive feature of Serial Attached SCSI is that this interface supports SAS and SATA drives, and both types of drives can be connected to the same controller at the same time. However, SAS drives cannot be connected to a SATA controller, since these drives, firstly, require special SCSI commands (Serial SCSI Protocol) to operate, and secondly, are physically incompatible with a SATA block. Each SAS drive connects to its own port, but it is still possible to connect more drives than the controller has ports. SAS-extenders (Expander) provide this possibility.

The original difference between a SAS disk header and a SATA disk header is an additional data port, that is, each Serial Attached SCSI disk has two SAS ports with its own original ID, thus the technology provides redundancy, which improves reliability.

SAS cables are slightly different from SATA, and there is a special cable accessory included with the SAS controller. Just like SCSI, hard drives of the new standard can be connected not only inside the server case, but also outside, for which special cables and equipment are provided. To connect "hot-swappable" disks, special boards are used - backplane, which have all the necessary connectors and ports for connecting disks and controllers.

As a rule, the backplane board is located in a special case with disk sled mounting, such a case contains a RAID array and provides its cooling. In the event of failure of one or several disks, it is possible to quickly replace a failed HDD, and replacing a failed drive does not stop the operation of the array - just change the disk and the array is fully functional again.

Adaptec SAS Adapters

Adaptec has presented two rather interesting models of RAID controllers for your consideration. The first model is a representative of the budget class of devices for building RAID in low-cost entry-level servers - this is the eight-port model ASR-48300 12C. The second model is much more advanced and designed for more serious tasks, it has eight SAS channels on board - this is the ASR-4800SAS. But let's take a closer look at each of them. Let's start with a simpler and cheaper model.

Adaptec ASR-48300 12C

The ASR-48300 12C controller is designed to build small RAID arrays of levels 0, 1 and 10. Thus, the main types of disk arrays can be built using this controller. Supplied this model in an ordinary cardboard box, which is decorated in blue and black, on the front side of the package there is a stylized image of a controller flying from a computer, which should evoke thoughts about the high speed of a computer with this device inside.

The scope of delivery is minimal, but includes everything you need to get started with the controller. The kit contains the following.

Controller ASR-48300 12C
. Low profile brace

. Storage Manager CD
. Brief manual
. Connecting cable with connectors SFF8484 to 4xSFF8482 and power supply 0.5 m.

The controller is designed for PCI-X bus 133 MHz, which is very widespread in server platforms. The adapter provides eight SAS ports, however, only four ports are implemented as an SFF8484 connector, to which drives are connected inside the case, and the remaining four channels are brought out in the form of an SFF8470 connector, so some of the drives must be connected from the outside - this can be an external box with four drives inside.

When using the expander, the controller has the ability to work with 128 disks in the array. In addition, the controller is able to work in a 64-bit environment and supports the corresponding commands. The card can be installed in a 2U low-profile server with the included low-profile blank. The general characteristics of the board are as follows.

Advantages

Cost-effective Serial Attached SCSI controller with Adaptec HostRAID™ technology for high performance critical data storage.

Client needs

Ideal for supporting entry-level, mid-range, and workgroup server applications that require high-performance storage and robust security, such as applications Reserve copy, web content, Email, databases and data sharing.

System Environment - Department and Workgroup Servers

System bus interface type - PCI-X 64 bit/133 MHz, PCI 33/66

External connections - One x 4 Infiniband/Serial Attached SCSI (SFF8470)

Internal connections - One 32 pin x 4 Serial Attached SCSI (SFF8484)

System Requirements - Server Type IA-32, AMD-32, EM64T and AMD-64

32/64-bit PCI 2.2 or 32/64-bit PCI-X 133 slot

Warranty - 3 years

RAID levels - Adaptec HostRAID 0, 1, and 10

Key features of RAID

• Support for boot arrays
• Automatic recovery
• Management with Adaptec Storage Manager software
• Background initialization

Board dimensions - 6.35cm x 17.78cm (including external connector)

Operating temperature - 0° to 50° C

Power dissipation - 4 W

Mean Time Before Failure (MTBF - time between failures) - 1692573 hours at 40 ºC.

Adaptec ASR-4800SAS

Adapter number 4800 is more functionally advanced. This model is positioned for faster servers and workstations. It supports almost any RAID arrays - arrays that are available in the younger model, and you can also configure RAID 5, 50, JBOD and Adaptec Advanced arrays data protection Suite with RAID 1E, 5EE, 6, 60, Copyback Hot Spare with Snapshot Backup option for tower and high-density rack servers.

The model comes in a package similar to the junior model with the design in the same "aviation" style.

The kit contains almost the same as the junior card.

Controller ASR-4800SAS
. Full size brace
. CD with driver and full manual
. Storage Manager CD
. Brief manual
. Two cables with connectors SFF8484 to 4xSFF8482 and power supply 1 m each.

The controller supports the 133MHz PCI-X bus, but there is also a 4805 model that is functionally similar but uses the PCI-E x8 bus. The adapter provides the same eight SAS ports, however, all eight ports are implemented as internal ones, respectively, the board has two SFF8484 connectors (for two bundled cables), however, there is also an external connector of the SFF8470 type for four channels, when connected to which one of the internal connectors turns off.

In the same way as in the younger device, the number of disks is expandable up to 128 using expanders. But the main difference between the ASR-4800SAS model and the ASR-48300 12C is the presence of 128 MB DDR2 ECC memory used as a cache on the first one, which speeds up work with the disk array and optimizes work with small files. An optional battery module is available to save data in the cache when the power is turned off. The general characteristics of the board are as follows.

Benefits - High performance storage and data protection connectivity for servers and workstations

Customer Needs — Ideal for supporting server and workgroup applications that require consistently high levels of read/write performance, such as video streaming, web content, video-on-demand, fixed content, and reference data storage.

• System Environment - Department and Workgroup Servers and Workstations
• System Bus Interface Type - PCI-X 64-bit/133 MHz host interface
• External connections - SAS connector one x4
• Internal connections - SAS connectors two x4
• Data Transfer Rate - Up to 3 GB/s per port
• System Requirements - Intel or AMD architecture with free 64-bit 3.3v PCI-X slot
• Supports EM64T and AMD64 architectures
• Warranty - 3 years
• Standard RAID Levels - RAID 0, 1, 10, 5, 50
• Standard RAID Features - Hot Spare, RAID Level Migration, Online Capacity Expansion, Optimized Disk, Utilization, S.M.A.R.T and SNMP support, plus features from Adaptec Advanced

• Data Protection Suite including:

1. Hot Space (RAID 5EE)
2. Striped Mirror (RAID 1E)
3. Dual Drive Failure Protection (RAID 6)
4. Copyback Hot Spare

• Advanced RAID Features - Snapshot Backup
• Board dimensions - 24cm x 11.5cm
• Operating temperature - 0 to 55 degrees C
• Mean Time Before Failure (MTBF - time between failures) - 931924 hours at 40 ºC.

Testing

Testing adapters is tricky business. Moreover, we have not yet acquired much experience with SAS. Therefore, it was decided to test the speed of hard drives with SAS interface in comparison with SATA drives. To do this, we used our existing 73 GB Hitachi HUS151473VLS300 15000rpm SAS drives with 16Mb buffer and WD 150GB SATA150 Raptor WD1500ADFD 10000rpm drives with 16Mb buffer. We made a direct comparison of two fast drives, but with different interfaces on two controllers. The disks were tested in the HDTach program, in which the following results were obtained.

Adaptec ASR-48300 12C

Adaptec ASR-4800SAS

It was logical to assume that a SAS hard drive would be faster than a SATA one, although we took the fastest WD Raptor drive for performance evaluation, which can compete in performance with many 15000 rpm SCSI drives. As for the differences between the controllers, they are minimal. Of course, the older model provides more features, but the need for them arises only in the corporate sector for the use of such devices. These enterprise features include special RAID levels and additional cache memory on board the controller. An ordinary home user is unlikely to install 8 hard drives assembled in a redundant RAID array in a home, even up to the very roof of a modified PC - rather, preference will be given to using four drives for a 0 + 1 array, and the rest will be used for data. This is where the ASR-48300 12C comes in handy. In addition, some overclocker motherboards have a PCI-X interface. The advantage of the model for home use is the relatively affordable price (compared to eight hard drives) of $350 and ease of use (inserted and connected). In addition, 2.5-inch 10K hard drives are of particular interest. These hard drives have lower power consumption, heat up less and take up less space.

conclusions

This is an unusual review for our site and is more about exploring user interest in specialty hardware reviews. Today, not only two unusual RAID controllers from the well-known and well-established manufacturer of server hardware, Adaptec, were considered. It is also an attempt to write the first analytical article on our website.

As for our today's heroes, Adaptec's SAS controllers, we can say that the next two products of the company were a success. The younger model, the $350 ASR-48300, may well take root in a productive home computer and even more so in an entry-level server (or a computer that performs its role). The model has all the prerequisites for this: convenient Adaptec Storage Manager software, support from 8 to 128 disks, work with basic RAID levels.

The older model is designed for serious tasks and, of course, can be used in low-cost servers, but only if there are special requirements for the speed of working with small files and the reliability of information storage, because the card supports all levels of enterprise-class RAID arrays with redundancy and has 128 MB fast DDR2 cache with Error Correction Control (ECC). The cost of the controller is $950.

ASR-48300 12C

Model advantages

• Availability
• Support from 8 to 128 disks
• Ease of use
• Stable work
• Reputation

• PCI-X slot - for greater popularity, only support for the more common PCI-E is missing

ASR-4800SAS

• Stable work
• Manufacturer reputation
• Good functionality
• Availability of upgrades (software and hardware)
• Availability of PCI-E version
• Ease of use
• Support from 8 to 128 disks
• 8 internal SAS links

• Not very suitable for budget and home use sectors.