SAS interface.
The SAS or Serial Attached SCSI interface provides connectivity over a physical interface, similar to SATA, devices, command set-driven SCSI. Possessing backward compatible with SATA, it makes it possible to connect any devices controlled by the SCSI command set via this interface - not only hard drives, but also scanners, printers, etc. Compared to SATA, SAS provides a more developed topology, allowing parallel connection of one device over two or more channels. Bus expanders are also supported, allowing you to connect multiple SAS devices to a single port.
The SAS protocol is developed and maintained by the T10 committee. SAS was designed to communicate with devices such as hard drives, optical drives, and the like. SAS uses a serial interface to work with directly connected drives, compatible with the SATA interface. Although SAS uses a serial interface as opposed to the parallel interface used by traditional SCSI, SCSI commands are still used to control SAS devices. Commands (Fig. 1) sent to the SCSI device are a sequence of bytes of a certain structure (command descriptor blocks).
Rice. one.
Some commands are accompanied by an additional "parameter block" that follows the command descriptor block, but is already passed as "data".
A typical SAS interface system consists of the following components:
1) Initiators. An initiator is a device that originates service requests for target devices and receives acknowledgments as requests are executed.
2) Target Devices. The target device contains logical blocks and target ports that receive service requests and execute them; after the processing of the request is completed, a confirmation of the request is sent to the initiator of the request. The target device can be either a single hard drive or an entire disk array.
3) Data delivery subsystem. It is part of the I / O system that transfers data between initiators and target devices. Typically, the data delivery subsystem consists of cables that connect the initiator and the target device. Additionally, in addition to cables, the data delivery subsystem may include SAS extenders.
3.1) Expanders. SAS extenders are devices that are part of the data delivery subsystem and make it possible to facilitate data transfers between SAS devices, for example, allowing you to connect several target SAS devices to one port of the initiator. Connecting through an extender is completely transparent to target devices.
SAS supports connecting SATA devices. SAS uses a serial protocol to transfer data between multiple devices and thus uses fewer signal lines. SAS uses SCSI commands to manage and communicate with target devices. The SAS interface uses point-to-point connections - each device is connected to the controller by a dedicated channel. Unlike SCSI, SAS does not require the user to terminate the bus. The SCSI interface uses a common bus - all devices are connected to the same bus, and only one device can work with the controller at a time. In SCSI, the speed of information transfer on different lines that make up the parallel interface can vary. The SAS interface does not have this shortcoming. SAS supports a very large number of devices, while SCSI supports 8, 16, or 32 devices on the bus. SAS supports high data rates (1.5, 3.0, or 6.0 Gbps). Such a speed can be achieved by transferring information on each connection, while on the SCSI bus, the bus bandwidth is divided between all devices connected to it.
SATA uses the ATA command set and supports hard drives and optical drives, while SAS supports a wider range of devices, including hard drives, scanners, and printers. SATA devices are identified by the port number of the SATA interface controller, while SAS devices are identified by their WWN (World Wide Name) identifiers. SATA devices (version 1) did not support command queues, while SAS devices support tagged command queues. SATA devices since version 2 support Native Command Queuing (NCQ).
SAS hardware communicates with target devices on several independent lines, which increases the fault tolerance of the system (the SATA interface does not have this capability). At the same time, the SATA version 2 interface uses port duplicators to achieve a similar capability.
SATA is predominantly used in non-critical applications such as home computers. The SAS interface, due to its reliability, can be used in mission-critical servers. Error detection and error handling is much better defined in SAS than in SATA. SAS is considered a superset of SATA, and does not compete with it.
SAS connectors are much smaller than traditional parallel SCSI connectors, allowing SAS connectors to be used to connect 2.5" compact drives. SAS supports data transfer rates from 3 Gb/s to 10 Gb/s. There are several options for SAS connectors:
SFF 8482 is a variant compatible with the SATA interface connector;
SFF 8484 - internal connector with dense packing of contacts; allows you to connect up to 4 devices;
SFF 8470 - connector with dense packing of contacts for connecting external devices; allows you to connect up to 4 devices;
SFF 8087 - reduced Molex iPASS connector, contains a connector for connecting up to 4 internal devices; supports 10 Gbps;
SFF 8088 - reduced Molex iPASS connector, contains a connector for connecting up to 4 external devices; supports 10 Gbps speed.
The 8482 SFF connector allows you to connect SATA devices to SAS controllers, eliminating the need to install an additional SATA controller just because you need to connect a DVD burner, for example. Conversely, SAS devices cannot connect to the SATA interface, and a connector is installed on them to prevent them from connecting to the SATA interface.
Oh, Seagate is not on you;). I saw an excellent presentation about the differences between SAS and SATA from Igor Makarov from Seagate. I try to be brief and to the point.
There are several answers from different angles.
1. In terms of protocols, SAS is a protocol aimed at maximum flexibility, reliability, functionality. I would compare SAS to ECC technology for memory. SAS is with ECC, SATA is without. An example is the following unique features (compared to SATA).
- 2 full duplex ports on SAS devices as opposed to one half duplex on SATA. This makes it possible to build fault-tolerant multi-disk topologies in data storage systems.
- end-to-end data protection T.10. - a set of SAS algorithms that allows using checksums to be sure that the data prepared for recording is written to the device without distortion. And read and transmitted to the host without errors. This unique feature allows you to get rid of the so-called silent errors, that is, when erroneous data is written to the disk, but no one knows about it. Errors can appear at any level. Most often in buffers in RAM during transmission and reception. Silent errors are the scourge of SATA. Some companies claim that on a SATA drive with a capacity of more than 500 GB, the probability of data corruption in at least one sector is close to one.
- we talked about multipassing in previous answers.
- T.10 zoning - allows you to split the SAS domain into zones (of the VLAN type, if such an analogy is closer).
- and many many others. I brought only the most well-known features. Who cares - read the SAS / SATA specifications
2. Not all SAS drives are the same. There are several categories of SAS and SATA.
- so-called. Enterprise SAS - typically 10K or 15K rpm. Volumes up to 1 TB. Used for DBMS and speed-critical applications.
- Nearline SAS - usually 7.2K, volumes from 1 TB. The mechanics of such devices is similar to Enterprise SATA. But still two ports and other charms of SAS. Used in enterprises where large volumes are needed.
- Enterprise SATA, sometimes RAID edition SATA - almost the same as NL SAS, only single port SATA. Slightly cheaper than NL SAS. Volumes from 1 TB
- Desktop SATA - what is put in the PC. The cheapest and lowest quality discs.
The first three categories can be arrayed on controllers from LSI and Adaptec. The last one is absolutely impossible. You won't have problems later. And not because we have a cartel, but because the disks are designed for different tasks. That is 8x5 or 24x7, for example. There is also such a thing as the maximum allowable delay, after which the controller considers the disk to be dead. For desktop drives, it is many times larger. This means that under load, desktop SATA workers will “fall out” of the array.
In short, focus on specific lines for specific tasks. It is best to look at the manufacturers' websites. There are, for example, special low-noise and low-heating screws for home electronics.
The same approaches to SSD, but the area is still not formed, so there are a lot of subtleties. Here we focus on parameters. Although everything that is said in paragraph is true for SSD.
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 about 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 to 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 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 (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 bandwidth of 320 MB / s from 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 1.5Gb/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 (today 300 MB/s), 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 the 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 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 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: 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 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 above all, then 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 has been reduced to a minimum. 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 models in 36.7GB, 73.4GB, and 146 GB (with one, two and four plates).
Fluid dynamic bearings have also 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 server-grade motherboards 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 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 are simple activity LEDs, 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 for the RAID modes, the SAS RAID 4800 easily overtakes the "little brother" here: by default, RAID levels 0, 1, 10, 5, 50 are supported 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. 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 Adaptec AIC-7902B Ultra320 Adaptec 48300 8 port PCI-X SAS Adaptec 4800 8 port PCI-X SAS LSI Logic SAS3442X 8 port PCI-X SAS |
| 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 is indeed a promising technology. If you refer to the SAS technical documentation, you will understand why. This is not only the successor to serial SCSI (fast, convenient and easy to use), but also an excellent level of scalability and infrastructure growth, in comparison with which Ultra320 SCSI solutions seem 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, the latest models of storage and equipment, 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. | |
In modern computer systems, 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 HDD, then, despite the different technical characteristics and connectors, there are no cardinal differences between the devices. Backward one-way compatibility makes it possible to connect disks to the server board both via one and 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 are accessing the former at the same time and many tasks are being solved, 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
| SAS | SATA |
| For server systems | Primarily for desktop and mobile systems |
| Uses the SCSI command set | Uses the ATA command set |
| Minimum spindle speed HDD 7200 RPM, maximum - 15000 RPM | 5400 RPM minimum, 7200 RPM maximum |
| Supports checksum verification technology when writing data | A large percentage of errors and bad sectors |
| Two duplex ports | One half duplex port |
| Multipath I/O supported | Point-to-point connection |
| Command queue up to 256 | Command queue up to 32 |
| Cables up to 10 m can be used | Cable length no more than 1 m |
| Bus bandwidth up to 12 Gb/s (in the future - 24 Gb/s) | Bandwidth 6 Gbps (SATA III) |
| The cost of drives is higher, sometimes significantly | Cheaper in terms of price per 1 GB |
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 are still satisfying users of modern enterprise systems in terms of performance, but the growing need for higher speeds, higher data transmission integrity, reduced physical size, and wider standardization is calling into question the ability of a parallel interface without unnecessary costs to keep pace 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 is also associated 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, overcomes the existing limitations of parallel technologies in terms of performance, scalability, and data availability.
Multiple levels of compatibility
Physical CompatibilityThe 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 backplate 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 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 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.
