SAS hard disk

Features

SAS interface technology can be compatible with SATA. Specifically, both compatibility is mainly compatible with physical layer and protocol layers. In the physical layer, SAS interface and SATA interface are fully compatible, SATA hard drives can be used directly in SAS, and SATA is a sub-standard for SAS, so SAS controller can directly control SATA hard drive, but SAS However, it cannot be used directly in the SATA environment because the SATA controller does not control the SAS hard drive; in the protocol layer, SAS is composed of three types of protocols, and data transmission is performed using the corresponding protocol based on the connected different devices. Among them, serial SCSI protocol (SSP) is used to transmit SCSI commands; SCSI Management Protocol (SMP) is used to maintain the maintenance and management of the connection device; SATA channel protocol (STP) is used for transmission between SAS and SATA. Therefore, in the cooperation of these three protocols, SAS can be seamlessly bind to SATA and some SCSI devices.

SAS hard drive is the fastest speed in the mechanical hard disk, first, the SAS interface is fast than SATA and SCSI's mechanical hard drive, second plus speed fast, fast, so SAS hard disk is applied Read or write on diskless servers.

The backpanel of the SAS system can be connected to both a dual port, a high-performance SAS drive, or a high capacity, low-cost SATA driver. So the SAS driver and SATA drivers can exist at the same time in a storage system. However, it should be noted that the SATA system is not compatible with SAS, so the SAS drive cannot be connected to the SATA backplane. Due to the compatibility of the SAS system, users can use the hard drives of different interfaces to meet the needs of various applications on capacity or efficiency, so there is more flexibility when the storage system is expanded, allowing the storage device to maximize investment benefits.

In the system, each SAS port can connect up to 16256 external devices, and SAS takes a direct point-to-point serial transmission mode, the rate of transmission is as high as 3Gbps, and there will be 6Gbps and even after the estimation 12Gbps high speed interface appears. The SAS's interface has also been improved, and it offers 3.5 inches and 2.5-inch interfaces, so it is suitable for different server environment. SAS rely on the SAS expander to connect to more devices, SAS's expander is mostly 12-port, but according to board vendor product R & D plans, there will be 28, 36-port expander to introduce, to connect SAS equipment, host equipment Or other SAS expanders.

and traditional parallel SCSI interfaces, SAS is not only significantly improved on the interface speed (mainstream Ultra320SCSI speed is 320MB / sec, while SAS is just 300MB / sec, the future will reach 600MB / SEC Even more), and because the serial cable can be used, not only longer connection distance, but also improve the anti-interference ability, and this detailed cable can also significantly improve the heat dissipation inside the chassis.

Older Comments

SAS is mainly:

1) Hard disk, the control chip is small: only special cilia, Seagate, Mai Tuang and Fujitsu, etc. Not many hard disk manufacturers have launched SAS interface hard drives, too small varieties, and many other manufacturers' SAS hard drives in the product internal testing phase. In addition, the SAS controller chip or some SAS switching cards are not much, mostly in LSI and Adaptec.

2) Hard disk price is too expensive: SAS hard drives are more expensive than the same capacity Ultra320scsi hard drive. The price that has always been highly affects the number of users' purchases and the number of channels of digestion, and cannot form large quantities of SAS hard drives. The pressure of their cost will continue to cause prices to fail. If the user wants to be a simple RAID level, then not only need to purchase multi-SAS hard drive, but also buy expensive RAID cards, the price is basically comparable to the hard disk.

SAS Detailed (14)

3) The actual transmission speed is not large: the interface speed of the SAS hard disk does not represent the data transfer speed, subject to the hard disk mechanical structure, SAS hard disk The mechanical structure is almost the same as the SCSI hard drive. The bottleneck of data transmission is concentrated in the hard disk internal mechanism and hard disk storage technology, the internal data transfer speed determined by the disk speed, that is, 80MBSEC, the performance improvement of the SAS hard disk is not obvious.

4) Users pursue mature, stable products: From the products that have been launched, more SAS hard drives are applied to high-end 4-way servers, while 4-way server users are not a high speed Hard disk interface technology, most attracting them should be mature, stable hardware products, although SAS interface servers and SCSI interface products are similar in speed, stability, but technology and products are not mature enough.

However, with hard disk manufacturers, Seagate and other hard disk manufacturers, Seagate and other hard disk manufacturers and many server manufacturers, SAS-related product technology will gradually mature, and the price will gradually slip, sooner or later. Become a mainstream interface of the server hard drive.

At this stage, it has become the mainstream interface of the cloud server service provider.