【 Weak current College 】 various hard disk interface protocol analysis

Hard drive interface is the hard drive and the connection between the host system, function is the hard disk cache and transfer data between the host memory. Different hard drive interface type determine the hard disk and controller connection speed, throughout the system, the performance of the hard drive interface on the overall performance of disk arrays have a direct impact, so understanding a disk array disk interface often is the product of one of the key indicators. Storage system currently widespread application of hard drive interface protocol including SATA, SCSI, SAS and FC, besides ATA hard drives on SATA hard drive before it appears in some low-end storage systems are widely used.

Each hard drive interface protocol has different specifications, have different transmission speeds, their access efficiency difference is large, the practical applications and target market. At the same time, the hard disk interface agreement at the stage of technology life vary, some have disappeared and face out, some are promising, but the development is not yet mature. So often plagued by customers is how to choose the right type of the array, you can meet the application performance requirements, and can reduce the overall cost of the investment. Now, we will take you through the current common hard drive interface technical differences and characteristics to help you choose the best fit for your needs.

ATA, in a parallel decline in the

ATA (ATAttachment) hard drive interface protocol standard IDE hard drive (IntegratedDriveElectronics) of specific interface standard. Since its inception, has been its cheap, good stability, high standardization, won the majority in the low-end customers, even in some high end applications, such as server applications also have a certain market. ATA specifications including the ATA/ATAPI-6 which UltraATA100 compatible previous ATA version, at the splices 40-pin uses standard 16-bit parallel data bus and 16 control signal.

The first hard drive interface protocol are parallel ATA (ParalleATA) hard drive interface protocol. PATA interfaces generally use 16-bit data bus, each bus processing transfer 2 bytes. PATA interface typically 100Mbytes/sec bandwidth, data bus must lock in 50MHz, in order to reduce the filter design complexity, PATA use Ultra bus, through the "double data rate" or 2 edge (rising and falling edge) clock mechanism used to perform DMA transfers. This data filtering rising and falling edge is collecting data on the lower half of the required filter frequency. This bandwidth is: 25MHz clock frequency x2 double clock frequency x16 bits per each edge/8 bits/byte = 100Mbytes/sec.

In the past 20 years, PATA ATA hard drive interface as a mainstream technology. But with the CPU clock frequency and the continuous improvement of memory bandwidth, PATA gradually appear insufficient. On the one hand, the hard disk manufacturing technology matures the ATA hard drive unit prices gradually to reduce, on the other hand, due to parallel bus interface, the transmission of data and signal bus is reused, so transfer rates are subject to certain restrictions. If you want to increase the transfer rate, then the transfer of data and signal tends to cause interference, thereby causing the error.

PATA's technology potential seems to have come to an end, but in today's many large enterprises, PATA existing transfer rate has gradually cannot meet the needs of users. People urgently look forward to a more reliable, more efficient hard drive interface protocol instead of PATA, driven by demand, serial (Serial) ATA bus interface technology came into being, a direct result of the decline of the traditional technique of PATA.

FC, the cornerstone of high-end applications

Fibre Channel standards are American National Standards Institute (ANSI), is the industry standard interface. Usually people think it is a system with the system or systems and subsystems of the interconnection framework that peer-to-peer (or Exchange) is configured in the system using fiber optic cable connection. Of course, it is envisaged that in many of its formulation of the hard disk interface protocol, only the IPI (intelligent peripheral interface) and IP (Internet Protocol) in the URLconf is ideal.

Later fibre channel development include electronic (non-optical), and can be used relatively low-cost approach will include hard drives, many devices connected to the host port. On this large fibre channel standards set a supplement called fibre channel arbitrated loop (FC-AL). FC-AL make fibre channel hard drive is connected directly as for high-throughput interface performance-intensive system designers a path to improve i/o performance level. Current high-end storage products used are FC hard drive interface protocol of the hard disk.

FC hard disk name because through optical physics channel, therefore, IOI-fibre hard drive, now also supports copper wire physical channels. Like IEEE-1394, FibreChannel actually defined as SCSI-3 hard drive interface protocol standard for a class that belongs to the SCSI fellow brothers. As a serial interface FC-AL peak can achieve 2Gbits/s or even 4Gbits/s. And optical connection device maximum transmission distance can reach 10KM. By FC-loop can connect to 127 devices, that is why FC hard disk based storage devices in General can connect hundreds or even thousands of bright star in the hard disk provides large memory space.

About fibre hard drive interface protocol for its superior performance, stable transmission, enterprise storage for high-end applications play an important role. Industry-wide focus to the bandwidth of fiber optic interface. The first universal use of optical fiber interface bandwidth of 1 GB, then 2Gb bandwidth fibre products dominate the markets have up to three years time. Now the latest bandwidth standard is 4Gb, meshFormer General manufacturers have already introduced new Gartner 4Gb related, then the predicted 4 GB fibre products in the next 2 years will be 300% annual compound growth rates and rapid growth, and in 2007 to replace the 2 GB fibre into mainstream markets.

For this report views, the views of the industry. Some people think that 2 GB Fibre Channel formally replace 1Gb also only less than 3 years, suppliers and immediately launch the 4 GB of products, the enterprise acceptance of doubtful. On the other hand, disk interface-the rise of SAS technology, and host interface-iSCSI technology development, but also to the development of optical storage pressure.

In fact, 4 GB Fibre Channel Transport Protocol as early as 2002 has passed the American National Standards Institute (ANSI) fibre channel entity interface (FibreChannel-PhysicalInterfaces, hereinafter referred to as FC-PI) hard drive interface protocol specification, while at the same time, 10Gb optical standards are also published in the same year, but because 10Gb fibre does not have the ability to backward compatibility, user if you want to upgrade to 10Gb optical platform, you must replace all the infrastructure, the cost is too expensive, too.

In comparison, 4Gb is 2 GB as the basis for the extension of the transmission protocol can be backward compatible with 1Gb and 2 GB, the use of fiber optic wires, connection ports are the same, meaning that users in the import 4Gb device, without the need for compatibility issues with the replacement of old equipment, not only can protect existing investments, or you can take an incremental upgrades, phasing out the old 2 GB device. At present, the storage vendor's 4 GB fibre products and 2 GB fibre products have no price gap, the user can phase almost of purchase to the 4 GB fibre products, in this sense, the 4 GB fibre products popularity is also just around the corner.

Hard drive interface protocol for on-demand, flexible choice

Network storage device are broadly classified into three categories, namely high-end and mid-range and near-line (Near-Line). Currently, high-end storage products are mainly used for fibre channel hard disk drive, applied to the critical data in real time of storage capacity. Midrange storage devices are SCSI hard-disk interface protocol, applied to business-critical data for mass storage. Near-line is the recent emerging storage areas, generally use the SATA hard disk storage, applied to a non-critical data in bulk storage, aims to replace the previously used tape data backup.

The next few years, fibre channel and SAS will be stored on the preferred interface, both of these techniques in real-world performance on almost the same. However, from a development perspective, in about a year later, SAS hard drive interface protocol transmission bandwidth is also possible to double and fibre channel to the next step is to 8Gbps or 10Gbps there is as yet no conclusive, and development to 8Gb or 10Gb, backward compatibility problems have not been effectively addressed.

At present, the technology better, fibre or SAS, is still difficult to judge. However, due to parallel SCSI occupies 80% of enterprise hard drive market, and SAS, SATA hard disk compatible with the low-end. So when the user of tight budgets, you can select a mix of SATA drives; when performance is the first time, you can replace a high-performance SAS drives. Thus, according to Fujitsu company forecasts: in the next few years, SAS will likely occupy most of the high-end storage market.

FC, SCSI, and SAS interface protocols market scale forecasts

For users: simple comparison hard drive does not have to be expensive, the better, the key is to see if it suits your application. In addition pure hard drive hard drive interface protocol is not a measure of a storage system performance indicators of unique elements, in addition to the hard disk performance, storage system hardware design, front-end host interfaces, and other performance indicators is also on the overall performance of the storage system the tremendous impact. If you need to apply to the i/o load lighter applications such as file sharing, FTP, audio storage, data backup, you can consider arrays based on SATA hard drive. If the i/o load heavier VOD, FTP, EMAIL, Web, database, application, consider using SCSI/SAS hard disk storage system; if you are a massive data center, the number of demand huge hard disk, taking into account the current SAS technology is mature, we still recommend selection based on fibre hard disk storage system.

SATA, the low-end wandering

PATA has low-end storage applications over the years of glory, but due to their technical limits, gradually being serial bus hard drive interface protocol (SerialATA, SATA) alternative. SATA to its serial data send mode. In the process of data transfer, data cable and signal wire independent use and transfer of clock frequency remain independent, compared with the previous PATA, SATA transfer rate can reach 30 times in parallel. You can say: SATA technology and is not a simple sense of PATA technology, which is a new bus architecture.

From the bus structure, SATA hard drive interface protocol used to transmit data for a single path or sequence of bit to transfer, the second path to return the response. Control information using predefined bits to transmit, and distribute the data center to a packaged format for use on/off signal pulse is sent, so you don't need another transmission lines. SATA @ 16-bit. Parallel UltraATA bus each clock frequency transmission 16bit data, but only the 1bit SATA, but serial bus can higher transmission speed to compensate for the loss of serial transmission. SATA will introduce 1500Mbits/sec bandwidth or 1.5Gbits/sec bandwidth. Since the data used 8b/10b encoding, the effective maximum transmission peak is 150Mbytes/sec。

At present to be able to see a SATA-1 and SATA-2 two standards, the corresponding transfer speeds are 150MB/s and 300MB/s. From this point, the speed of SATA hard drive the PATA has gone far behind rejection. Secondly, from the point of data transfer, SATA-PATA stronger anti-interference ability. From SATA Committee published information by 2007, in the third generation of serial ATA technology, personal computer storage system will have a maximum 600MB/s of data bandwidth. In addition, the serial data line only takes 4-needle structures, compared with parallel installation with more convenient, more conducive to reducing chassis cable, enabling cooling.

Parallel ATA and SATA hard drive interface protocol comparison

Although manufacturers generally claimed that support hot-swap SATA, but in fact, SATA hard disk damage, cannot like SCSI/SAS and FC hard drive, display specific damage to the hard disk so that the hot-plug feature is useless. At the same time, although in many performance SATA is far superior to PATA, even in some single thread task tests, has not lost to SCSI performance, however it's still as low-end machine chassis design of the application, in the face of big data throughput or multi-threaded transfer tasks, compared to SCSI hard drive, and still look great. In addition to speed, multi-threaded data when read, HDD frequently fro so hard drive overheat is SATA needs to overcome deficiencies. It is because of these technical defects caused fatal, so far, it can only be used in the low-end SATA storage applications.

SCSI hard drive interface protocol, midrange storage for mainstream choice

SCSI (SmallComputerSystemInterface) is a specialized computer system design for small storage unit hard drive interface protocol mode is typically used for business-critical server to assume a larger store load, prices are more expensive. SCSI computers can send commands to a SCSI device, disk you can move the drive arm positioning head, in the media and pass data in the cache, the entire process in the background. You can also send several commands at the same time, suitable for high i/o load. On the disk array of overall performance is significantly higher than the array based on ATA hard drives.

SCSI hard drive interface protocol specification development to today, is the sixth-generation technologies, from the newly created when SCSI (8bit) to today's Ultra320SCSI, speed from 1.2MB/s to 320MB there a qualitative leap. Current mainstream SCSI hard disks are Ultra320SCSI interface can provide 320MB/s interface speed. SCSI hard drive also has specialized support hotplug technologies SCA2 interface (80-pin), and SCSI backplane, you can easily drive hot swap. In workgroup and departmental servers, hot-plug feature is almost a must.

Compared to the ATA hard drives, SCSI hard disk interface protocol reflect a more appropriate, high-end storage applications of technology advantages:

The first SCSI hard disk relative to ATA interfaces support a greater number. In General, the ATA hard drives with IDE slot and system connections, and each IDE slot is occupied an IRQ (interrupt), with each two IDE devices will occupy an IDE can road, although additional IDE controller card, you can increase the number of IDE devices supported, but the total number of connected IDE device cannot exceed a maximum of 15. While all of the SCSI device occupies only one interrupt (IRQ), therefore it supported disk expansion of greater than ATA. The advantages for the ordinary user, not too attractive, but for enterprise storage applications is remarkable, some organizations require almost uncontrolled expansion disk system capacity to meet the needs of users of network storage.

Next: SCSI bandwidth is wide Ultra320SCSI can support a maximum bus speed 320MB/s, although this is just a theoretical value, but in the actual data transfer rates, fastest ATA/SATA hard disks compared to SCSI hard drive both stability and transmission rate, there is a gap. However, if the sheer speed of perspective, the user may not need to select the SCSI hard drive, RAID technology can more effectively improve the transfer speed of the disk.

Finally, SCSI hard drive CPU utilization is low, and parallel processing capability. The ATA and SATA hard disk while also enables multi-user simultaneous access, but when parallel processing more than a certain number, ATA/SATA hard drive would have revealed a large I/O flaws, rates have dropped significantly. At the same time, the hard disk head fro, resulting in hard disk heat instability phenomenon.

For SCSI hard-disk interface protocol is concerned, it has a separate chip is responsible for data processing, when the CPU instruction transmitted to SCSI, immediately go to handle subsequent directives, other related work to SCSI controller chip to process; when SCSI "processor" when processing is complete, send control information again to the CPU, CPU and then proceeded to carry out follow-up work, therefore it is not difficult to imagine a SCSI system CPU utilization is low and SCSI hard drives allows a user to data transmission at the same time, another user at the same time for data lookups, this is the SCSI hard disk parallel processing capability.

SCSI hard drive more expensive, but higher quality performance, its unique technological advantages ensure SCSI hard drive interface protocol has been in the midrange storage market in occupies the position of the tower. Common ATA hard drive speed is 5400 or 7200RPM; SCSI hard drive is 10000 or 15000RPM, SCSI hard drive's warranty period can reach 5Years, the average non-fault time 1,200,000 hours. However for enterprises, while SCSI in transfer rate and fault tolerance with excellent performance, but its expensive price allows users. And the next generation birth of SAS SCSI technology, better compatibility with dual performance and price advantage.

SAS hard drive interface protocol of tomorrow's Empire

SAS is the abbreviation for that SerialAttachedSCSI serial attached SCSI. And now the popular SerialATA (SATA) hard drives are the same, and are based on serial technology for higher transmission speed, and by shortening the link line to improve the internal space, etc.

SAS hard drive interface protocol is a new generation of technology, with SATA SCSI to PATA's revolutionary significance, SAS is also one of the SCSI technology change in sexual development. It has been used in practice and validate SCSI functions and features, and on this basis introduces SAS expanders. SAS can connect more devices, at the same time, due to its connector is relatively small, SAS can 3.5 inches or smaller 2.5 inch hard drives to achieve full dual port, this functionality was previously only in larger 3.5 fibre channel hard disk drive can be realized. This feature for high density servers such as blade servers and other applications require redundancy drive is important.

Investment for the protection of users, SAS hard drive interface protocol interface technology can be backward compatible with SATA. SAS system's back panel (Backplane) can be connected with a two-port, high-performance SAS drives, or high-capacity, low-cost SATA drives. In the past because of SCSI, ATA respectively occupy different market segments, and bandwidth can be shared between devices, interfaces, drivers, cables, are incompatible with each other, causing user resources scattered and isolated, increasing the total cost of ownership. And now, users even with different types of hard disk, you do not need to be reinvested, investment protection for corporate users, it is very meaningful. But it is important to note that the system is not compatible with SATA and SAS, SAS drives cannot be connected to the SATA backplane.

SAS hard drive interface protocol used by the Extender can have one or more of the SAS host controller connection more drives. Each Extender can connect a maximum of 128 physical connections, including other master connection, other SAS Expander or hard drive. This highly scalable connection mechanism enables enterprise-level mass storage space requirements, and can easily support multiple-point cluster for automatic recovery feature or load balancing. Currently, 3Gbps SAS interface speed, its SAS expanders for 12 port. Soon, there will be a 6Gbps even high-speed interface 12Gbps, and there will be 28 or 36-port SAS Expander appears in order to adapt to different application requirements. The actual use of the performance is comparable to the foot to the fiber.

Although born SCSI SAS, but due to its outstanding suitable for high-end application performance advantages, more commonly the SAS and fibre technology. As a result of the development by the SCSI SAS, in the host-side will have a large number of manufacturers compatible. SAS using point-to-point connections, each providing SAS ports, transport capacity 3Gb bandwidth and 4 GB Fibre desserts, this kind of transport not only improves the high reliability and fault tolerance, but also increases the overall system performance. In the disk-to-end, SAS hard drive interface protocol of Exchange domain can provide 16384 node, while fibre loop contains up to 126 nodes. And compatible with SATA disks as embodied in the extensibility is another significant SAS advantages for different business applications, disk-to-end users have the flexibility to select a different storage medium, on-demand reduces costs for users.

These SAS interfaces have unique advantages while SAS product cost, starting from the chip-level are far lower than FC, but it is precisely because SAS outstanding price/performance advantages that enable SAS disk interface areas, to bring great optical storage. There are already numerous manufacturers launch support SAS hard drive interface protocol products, although not yet widespread in the user level, but has begun to SAS products tribe. SAS become next generation storage interface standard, of mainstream success hard drive interface protocol of splendid have been foreseeable.