SAS connector: types, features and photos

SAS Serial Attached SCSI is based on the SCSI concept. Historically, SCSI has not been used so often in computing. It is mainly used in server systems and other fields, such as fiber optic connections to storage systems. SAS, unlike SSD, is not a data carrier, but a connection interface that sends large amounts of information with different transfer rates. SAS and SATA drives are very similar, differ only in connectors. Therefore, you need to learn to distinguish between a storage system (SSD or HDD) and connection interfaces for these systems before connecting a SAS disk to a SATA connector.

Protocol Development History

The name SATA comes from the Serial Advanced Technology Attachment and is a replacement for the old PATA (Parallel ATA), known as ATA or IDE. Computers of the 80s or earlier models were equipped with disks with SAS-connectors with “strips” of 40 contacts, which allowed connecting up to two devices - one master and another slave. Adjustment was carried out by tiny jumpers.

The difference between the two technologies is that the method for moving bits on SATA drives is sequential rather than parallel, although the protocol used for transfer is the same in both cases. Even if the “language” they speak is the same, the transmission of information is different. In one case, the bits go one after another (series), and in the other - in groups of 16 (in parallel).

In addition to the small difference between the connectors, the difference between the two technologies lies in the communication protocol, so the SAS disk does not directly connect to the controller, which is taken into account before connecting the SAS disk to the SATA connector. One of the requirements of the SAS system is that it can work with attached SATA drives, although access to it leads to reduced performance.

There is a type of drive called SAS-NL or Nearline SAS that has a SAS connection between the drive and the controller, but the mechanical part is the SATA drive. The idea behind these drives is to provide quick access with minimal cost, since SAS drives are usually more expensive than SATA drives.

Serial Attached SCSI Interface

The SAS interface is the most unknown for the general public, since its use was distributed exclusively in the field of corporate storages and mass servers, despite the fact that its development is similar and very close to SATA.

As in the case of SATA, the SAS interface replaced the SCSI (Small Computer System Interface) standard, which was present on most servers of that time and became low-power for the huge flow of information needed for network services and increasing the number of connected devices. The emergence of the SAS interface has increased the speed of information transfer and at the same time connect a larger number of peripheral elements.

The SAS interface in the third version has a bandwidth of 3 Gb / s in the first version of SAS-1, up to 6 Gb / s in SAS-2, 12 Gb / s in SAS-3 and 24 Gb / s for its next version of SAS-4 .

With a higher data transfer rate, the SATA drive connection scheme in the SAS connector doubles the SATA drive cache from 64 MB to 128 MB. Thus, the buffer is always ready to send information, and sometimes hybrid cache systems are used, which, in addition to traditional cache chips, also use NAND memory to speed up the sending of information.

In SAS blocks, data is the most important, therefore, these disks have more advanced systems for protection against information loss, which makes them safe and reliable. SAS and SATA connectors are physically very similar, although there are some differences between them, and so that they do not lead to connection errors, they must be taken into account before connecting a SATA drive to SAS.

SCSI Standards

SCSI (Small Computer System Interface) is a microprocessor-controlled intelligent bus that allows you to add up to 15 peripheral devices to your computer. It can be hard drives, scanners, printers and other peripheral devices. High-performance single SCSI cards have two controllers and support up to 30 peripherals on a single expansion card. The advantage of SCSI is that you can connect multiple elements to the host adapter using only 1 slot on the bus.

SAS is the latest standard trying to switch to a serial interface from parallel. All standards are parallel interfaces, that is, there are several wires and SAS connectors nearby. This means that SAS will be the first incompatible SCSI standard, at least when it comes to the connector.

It is designed to use the best features of SCSI, Serial ATA and Fiber Channel drives, it has some compatibility with SATA in only one direction. The SAS controller recognizes the SATA drive, but it does not recognize the SAS drive. Transmission speeds start at 3 Gb / s, and the standard requires an increase to 10 Gb / s.

Serial connection of devices

SCSI devices are connected in series. The external ones have two ports, one for the incoming cable and the other for the outgoing to the next element. The internal device has a port that connects to a ribbon cable with multiple SAS disk connectors. Some higher-end SCSI cards may have multiple internal ports.

SCSI has a unique identification number. You can usually set these numbers by pressing the jog dials on external devices or by setting the internal jumper. The SCSI identifier determines their order, which varies from 7 to 0 and from 15 to 8. By default, the host adapter has the highest priority - 7. You need to shut down the device at the end of the SCSI circuit by either setting the switch or by inserting the resistor module into the open port .

Usually host adapters are interrupted by default. If devices are connected both internally and externally, the user must remove the host adapter termination and apply the termination to the ends of both circuits. Adapters exist that allow you to connect SCSI peripherals through the parallel port. The data transfer speed through the parallel port is much lower than that of the SCSI host adapter, but it provides the ability to connect SCSI to laptops.

Not all devices can run on a parallel adapter, some have their own parallel port adapters. In general, when using a SCSI adapter, the parallel port will receive a transfer speed of about 1 Mbps.

Windows 95, 98, NT, Me, 2000 and XP, as well as most older Macintosh computers, provide internal SCSI support, while Windows 3.1 and DOS do not. Newer Macintosh computers support FireWire rather than SCSI for high-performance interfaces. To install SCSI on a computer running Windows 3.1 or DOS, you must add the appropriate driver.

Ideal interface add-ons

SCSI compatibility with SATA provides additional enterprise storage flexibility. Since their disks can share a common backplane and are housed in one enclosure, one SAS-based subsystem is capable of performing a wide range of corporate storage tasks: from highly accessible online storage to transferring data from disk to disk, backing up and storing at close range. Consolidating to a smaller number of more nationalized subsystems can save a significant amount of money and minimize placement, which will reduce the cost of servicing the IT storage.

In addition, developing organizations can purchase SAS cables, backplanes, and enclosures for initial use with SATA drives, making sure that such equipment does not expire when their storage needs expand and enterprise-class drives are in demand. SAS drives can simply be connected to existing storage subsystems.

Pinout Internal Connector

The pinout of the SAS connector is carried out for proper data transfer. SAS replaces the old Parallel SCSI and, like its predecessor, uses the standard SCSI command set. SAS offers optional compatibility with SATA version 2 and higher. This allows you to connect SATA drives to most SAS backplanes or controllers. Reconnecting them to the SATA backplane is not possible. There are over six different physical connector options. Pinout of the internal connector SAS SFF-8482.

System Integrator (SI)

The challenges that system integrators (SI) face when learning how to interact with technologies and components in order to get everyone to work together require experience. PMC-Sierra has put the system integrator (SI) in place of the interviewer. The SAS system socket is compatible with both the SAS HDD connector and the SATA HDD. However, a SATA socket with a printed circuit board (PCB) will not accept the SAS HDD connector.

The device includes several different mechanical configurations, such as:

• blade configuration with multiple drives on a sled;
• rack configuration with multiple drives on the backplane.

The Small Form Factor Committee (SFF), as part of the standards working group, identified several SAS drive slots for connecting to a printed circuit board.

The following options are available: right angle mounting, vertical mounting, panel mounting and cable. Two different external cables: 4-signal and 2-signal, were defined in the SFF Committee as basic. The 4X signal and circuit board receptacle are specified in SFF-8470. The signal 2x and two-row socket HSSDC2 are specified in SFF-8424.

Several internal cables are available for SAS. The first is 1x SAS / SATA and the connector specified in SFF-8482. The second available for internal connections inside the unit is the four-channel, indicated SAS connector in photo SFF-8484.

SAS vs SATA Drives

It should be remembered that both SATA and SAS are the connection interfaces that are integrated into the storage system, usually the HDD. However, the simple fact of enabling one of the two interfaces already determines the characteristics and performance of this unit.

SATA drives are more common and affordable. If the SAS interface has a large bandwidth through which large amounts of data can be transmitted simultaneously, it would be wasteful not to use it with storage systems capable of operating at a higher speed.

One of the main differences between hard drives using the SAS and SATA interface is that in the case of SATA, they spin at speeds from 5400 to 7200 rpm on the drives they use. The SAS interface does this at speeds from 10,000 to 15,000 rpm, which greatly improves final productivity.

Another major difference that is observed between SAS and SATA units is the high price-per-gigabyte ratio. A SAS drive with 15,000 rpm and 900 GB can cost about 420 euros (0.466 euro / GB), while a SATA drive with 7200 rpm and 1 TB (1024 GB) can cost about 45 euros (0.044 € / GB).

Not taking into account the huge difference in price, both systems are very uniform in terms of capabilities. The storage technology used for both interfaces is built on the same base and allows you to find drives up to 12 TB with a SATA or SAS interface.

SATA and SAS use full duplex switched point-to-point serial connections. There is no need to manually assign device identifiers or disconnect as in the case of Parallel SCSI. Both SATA and SAS provide high-speed connectivity, although care must be taken to avoid static discharge.

SATA data and power cables can be installed independently or as a connector. This latter configuration leads to confusion with the SAS connector, which looks similar to that connected to SATA.

Mini-SAS expansion cards supporting 4 or 8 ports are becoming quite popular for RAID (random array of independent disks) implementations, which provide both higher input-output performance and component redundancy.

Cable marking

The following table contains cable marking information that is designed to match the correct port of the component to which the cable end should be connected.

Mini-SAS HD Product Portfolio

Amphenol offers a mini SAS HD connector with optical cables for SAS 2.1 (6G) and SAS 3.0 (12G) protocols. It is equipped with a 2.9 mm diameter spiral optical cable that provides easy routing in any direction, as well as outputs that can accommodate either a direct fiber-optic output on the back of the connector or a rectangular output. Its length is from 5 to 100 meters.

Characteristics:

1. The internal and external connectors of the IMLA-based board ensure compliance with the electrical specifications of SAS 2.1 and the proposed 3.0.
2. 1X1, 1X2, and 1X4 connectors provide product family design flexibility.
3. All mini SAS HD connectors and board configurations fully comply with the requirements of 6G and 12G, which allows using the same part numbers when increasing the speed of the system from 6G to 12G.
4. Metal cages on the external connector and cables provide 360EMI.
5. A single-stage needle and cage connector provides continuous application to the circuit board.
6. External and internal cable assemblies are offered in 4x and 8x configurations with full matching EEPROM memory card.
7. External weakening of the cable leads to axial force.
8. The cable latch design reduces cable insertion and pairing problems.
9. Hybrid external cables from Mini-SAS HD to Mini-SAS provide backward compatibility with legacy system hardware.

The Amphenol ICC Mini-SAS High Density Connector System is the next generation SAS. It provides higher data rates and greater bandwidth.

The Amphenol ICC Mini-SAS Connector System provides twice the port density of current Mini-SAS connectors with 1 x 1 (4x), 1 x 2 (8x), and 1 x 4 (16x) port options. The Mini-SAS HD connector system has a two-row rectangular connector with a data rate of 12 Gb / s per channel. Each port handles 4 data bands with a speed of up to 48 Gbit / s with total bandwidth.

Features and benefits.

1. Compliance with SFF-8643.
2. Meets SAS 3.0 electrical specifications (12 Gb / s).
3. Connector system in 0.75 mm increments.
4. Improved signal integrity and minimization of crosstalk.
5. Eliminates the need for a mechanical key.
6. Card pinouts are easy with the existing Mini-SAS product.
7. The design of the press-in pin provides one-step placement on the printed circuit board.

Common Interface Disadvantages

There are cases when transferring data from SAS to SATA was useful. For example, using SAS disks for mass storage of information with low availability is a wasteful allocation of resources, and SAS backplanes will allow IT managers to seamlessly replace low-cost SATA disks for such storage applications. This represents a reasonable and cost-effective use in a corporate environment.

However, under the constant pressure of cutting IT budgets and enthusiasm for the obvious cost-performance advantages of SATA, some IT managers have begun deploying SATA drives for enterprises for which they are completely unsuitable. Any savings made by choosing SATA instead of SAS can be quickly erased due to loss of information, downtime and reduced performance. SATA , SAS .

Users should not be mistaken, although serial interfaces make them similar. SAS and SATA drives are very different. SAS drives are designed to operate under harsh conditions, and each component — a drive motor, spindle, drive, magnetic recording heads, control and servo processors, and embedded software — is specially designed and built for stress use.

SATA drives are an impressive example of smart design for high capacity at low cost, but they are incapable of meeting the performance and reliability standards of high-load storage applications.

Enterprise data warehouse has entered a new era, targeted solutions are now available to meet a wide variety of needs: from the most rigorous applications with high availability to cost-sensitive high-volume storage.

Choosing the “best” storage device is simply a matter of identifying needs and evaluating the capabilities of each potential solution. Serial Attached SCSI and Serial SATA have their place in the enterprise storage continuum.