SAS Market Trends for SAS Products

In the new generation of SAS-based application architectures, SAS and SATA enterprise hard drives are ideal storage components that complement each other's strengths. SAS hard drives are designed for high-demand and mission-critical applications, while SATA hard drives are suitable for nearline storage and other small and medium-sized business applications that have low storage requirements.

SATA is expected to replace SCSI drives with SATA in low-end storage systems this year, while Fibre Channel will be used in the majority of high- and mid-range external storage systems. However, factors such as the rapid decline in storage system prices have dramatically changed the industry's attitude toward SAS hard drives. In the trend of rapid decline in product prices, storage equipment manufacturers are bound to more cost-effective technology to manufacture storage devices, and SAS hard disk is precisely in line with this demand for products. In addition, the compatibility of SAS systems and SATA systems, as well as the implementation of the I-SCSI connection standard, will also promote the development of SAS systems.

Because the enterprise market has always been conservative about new technologies, perhaps SAS technology won't catch on as quickly as SATA technology, but it's only a matter of time. The former Maxtor expects that by 2009 two-thirds of external storage devices will use SAS technology to connect to SAS or SATA hard drives.

SAS hard drive applications

The responsiveness of the storage device, in addition to the cooperation between the various segments and the influence of the operating system, the responsiveness of the hard disk actually has a key position. Enterprise-level workstations or storage devices, in general, are using Fibre Channel (FC) and SCSI hard drives as the internal storage media. However, with the limitations of SCSI hard disks in terms of scalability, SAS (Serial Attached SCSI) hard disks have come to the fore. As server vendors increasingly use SAS drives as internal storage media, will SAS drives become a formidable rival to FC drives in the storage market?NetApp says that SAS drives can be used in small-load applications, where both budget and performance considerations apply.

Since SAS hard disks are more suitable for small load applications, what are the applications for small loads?NetApp explained, for example, in the 1,000 people below the e-mail system, or the scale of the ERP, CRM system, many domestic small and medium-sized enterprises are quite suitable. And like a large ERP, CRM system, or online real-time trading system, because the transmission volume is large, the response speed needs to be real-time fast, so it should still be used in a higher-end fiber-optic channel hard disk.

Serial Attached SCSI (SAS) SAS is a new generation of SCSI technology that uses the same serial technology as the popular Serial ATA (SATA) hard drives to achieve higher transfer speeds and to improve internal space by shortening the connection lines. SAS is a new interface developed after the parallel SCSI interface. This interface is designed to improve the performance, usability, and expandability of storage systems by providing compatibility with Serial ATA (abbreviated as SATA) hard disks. SAS interface technology is backward compatible with SATA, and the backplane of a SAS system can be connected to either dual-port, high-performance SAS drives or high-capacity, low-cost SATA drives. Because the ports of SAS drives and SATA drives look similar in shape, SAS drives and SATA drives can coexist in a single storage system. However, it is important to note that SATA systems are not SAS compatible, so SAS drives cannot be attached to SATA backplanes. Because of the compatibility of SAS, IT staff can utilize hard drives with different interfaces to meet the needs of various applications in terms of capacity or performance, thus providing more flexibility in expanding the storage system and maximizing the investment in storage devices.

The SAS interface technology is backward compatible with SATA, specifically the physical layer and protocol layer. In the physical layer, the SAS interface and the SATA interface are fully compatible, SATA hard disk can be used directly in the SAS environment, from the interface standard, SATA is a substandard of SAS, so the SAS controller can directly manipulate the SATA hard disk, but SAS can not be used directly in the SATA environment, because the SATA controller can not be SAS hard disk control. In the protocol layer, SAS consists of three types of protocols, which use the corresponding protocols for data transmission according to the different devices connected. Among them, Serial SCSI Protocol (SSP) is used to transmit SCSI commands; SCSI Management Protocol (SMP) is used to maintain and manage the connected devices; SATA Channel Protocol (STP) is used to transmit data between SAS and SATA. Therefore, with the cooperation of these three protocols, SAS can seamlessly integrate with SATA and some SCSI devices.

The backplane of a SAS system can be connected to either a dual-port, high-performance SAS drive or a high-capacity, low-cost SATA drive. So SAS drives and SATA drives can exist in a storage system at the same time. However, it should be noted that SATA systems are not SAS compatible, so SAS drives cannot be connected to SATA backplanes.


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In the system, each SAS port can connect up to 16,256 external devices, and SAS adopts a direct point-to-point serial transmission mode, with a transmission rate of up to 3Gbps, and it is estimated that there will be a 6Gbps or even 12Gbps high-speed interface in the future. SAS relies on SAS expanders to connect more devices, and the current expanders are mostly 12 ports, but according to the board manufacturer's product development program, there will be 28- and 36-port expanders introduced in the future to connect SAS devices, host devices, or other SAS expanders.

Compared with the traditional parallel SCSI interface, SAS not only in the interface speed to get a significant increase (now the mainstream Ultra 320 SCSI speed of 320MB / sec, and SAS is just starting speed of 300MB / sec, the future will reach 600MB / sec and even more), and because of the use of serial cables, not only can you The serial cables not only allow for longer connection distances, but also improve immunity to interference, and the thin cables significantly improve heat dissipation inside the chassis.

SAS current shortcomings are mainly the following:

1) hard disk, control chip variety is small: only Seagate, Maxtor, as well as Fujitsu and other hard disk drive manufacturers launched a SAS interface hard disk, too few varieties, most of the other manufacturers of SAS hard disk in the product internal testing stage. In addition, the peripheral SAS controller chip or some of the SAS adapter card is not much variety, most of the concentration in the hands of LSI and Adaptec.

2) Hard drive prices are too expensive: compared to the same capacity of the Ultra 320 SCSI hard drive, SAS hard drives are more than twice as expensive. Has been a high price directly affects the user's purchasing quantity and the number of channels to digest, and can not form a mass production of SAS hard disk, the pressure of its cost will, in turn, promote the price can not be reduced. If users want to do a simple RAID level, then not only do they need to buy multiple SAS hard drives, but they also need to buy an expensive RAID card, which is basically the same price as a hard drive.

3) The actual transfer speed does not change much: The interface speed of the SAS hard disk does not represent the data transfer speed, limited by the hard disk mechanical structure, now the mechanical structure of the SAS hard disk and SCSI hard disk is almost the same. The current bottleneck in data transfer is focused on the internal data transfer speed of the hard drive determined by the internal mechanical mechanism of the hard drive and the hard drive storage technology, disk speed, that is, about 80MBsec, the SAS hard drive performance enhancement is not obvious.

4)Users pursue mature, stable products: from the point of view of the products that have been launched, SAS hard disk is more often used in high-end 4-way servers, and more than 4-way server users are not the pursuit of high-speed hard disk interface technology, the most attractive to them should be mature, stable hardware products, although the SAS interface servers and SCSI interface products in the speed, stability Although SAS interface servers and SCSI interface products in terms of speed and stability are more or less the same, the current technology and products are not mature enough.

But with Intel and other motherboard chipset makers, Seagate and other hard disk manufacturers, as well as many server manufacturers to vigorously promote, SAS-related product technology will gradually mature, the price will gradually decline, sooner or later will become the mainstream interface of the server hard disk.

Summary

As a new storage interface technology, SAS is not only comparable to Fibre Channel in terms of functionality, but also has the ability to be compatible with SATA, and is therefore recognized by the industry as a good choice to replace parallel SCSI. According to VISUAL engineers, the advantages of SAS are mainly reflected in: flexibility, can be compatible with SATA, for users to save investment; scalability, a SAS domain can be directly connected to a maximum of 16,384 devices; excellent performance, point-to-point architecture so that the performance of the number of ports with the increase in the increase in the performance; a more reasonable cable design, to provide a more effective heat dissipation in high-density environments. There are usually four basic metrics to measure the strengths and weaknesses of a technology: performance, reliability, scalability, and cost. Looking back at the history of serial disk technology, from Fibre Channel, to SATA, to SAS, several technologies have their own strengths. Fibre Channel first appeared in the serialized storage technology, can meet the high performance, high reliability and high scalability of the storage needs, but the price remains high; SATA hard disk cost down, but mainly for near-line storage and non-critical applications, after all, in terms of performance and other aspects of poor; SAS should be regarded as an all-rounders, can support the SAS and SATA disks, it is very convenient to meet different cost-effective storage needs, is a high-performance, highly reliable and highly scalable solution.