SAS is the abbreviation of Serial Attached SCSI, and FC is the abbreviation of Fiber Channel.
Both protocols internally encapsulate SCSI packets, which include data and SCSI commands, including FCOE, FCIP, and SATA. The most internally encapsulated SCSI packets are because mechanical disks use SCSI commands.
FC disks generally add an FC adapter to the SCSI disk interface. FC storage is basically like this. There are many advantages to using FC disks. The biggest one is that the FC protocol can be organized using an arbitration loop. Disks, this can greatly increase the upper limit of the number of disks on one storage. Many mid- and low-end FC storages are organized in the arbitral ring method, and high-end storage is mostly organized in the Node method.
1. FC hard disk?
FC hard disk refers to a disk using FC-AL (Fiber Channel? Arbitrated? Loop, Fiber Channel Arbitrated Loop) interface mode. FC-AL enables Fiber Channel to be used directly as a hard disk connection interface, opening up a way for designers of high-throughput performance-intensive systems to increase I/O performance levels. Currently, high-end storage products use FC interface hard drives. ?
The name of FC hard disk is that it works through optical physical channels, so it is named fiber optic hard disk. It now also supports copper wire physical channels. Just like IEEE-1394, Fiber Channel is actually defined as a SCSI-3 standard and is a sibling of SCSI. As a serial interface, FC-AL peak value can reach 2Gbits/s or even 4Gbits/s. Moreover, the maximum transmission distance through optical connection equipment can reach 10KM. 127 devices can be connected through FC-loop, which is why storage devices based on FC hard drives can usually connect hundreds or even thousands of hard drives to provide large-capacity storage space. ?
About fiber optic hard drives, with their superior performance and stable transmission, they play an important role in high-end enterprise storage applications. The industry generally focuses on the bandwidth of optical fiber interfaces. The earliest widely used optical fiber interface bandwidth was 1Gb, and subsequently 2Gb bandwidth optical fiber products have dominated the market for three years. The current bandwidth standard is 4Gb, and currently most manufacturers have adopted 4Gb related products. 8Gb optical fiber products will also replace 4Gb optical fiber and become the mainstream of the market in the near future. ?
4Gb is a transmission protocol based on 2Gb. It can be backward compatible with 1Gb and 2Gb. The fiber optic cables and connection ports used are also the same, which means that when users import 4Gb equipment, they will not It is necessary to replace old equipment due to compatibility issues, which can not only protect existing investments, but also adopt a gradual upgrade method to gradually phase out old 2Gb equipment. ?
2. SAS hard disk?
SAS is the abbreviation of Serial Attached SCSI, that is, serially connected SCSI. Like the popular Serial ATA (SATA) hard drives, they all use serial technology to obtain higher transmission speeds and improve internal space by shortening the connection cable. SAS is a new generation of SCSI technology. SAS is a new interface developed after the parallel SCSI interface. This interface is designed to improve the performance, availability and scalability of the storage system and provide compatibility with Serial ATA (Serial ATA, abbreviated as SATA) hard drives. ?
SAS technology also has the advantage of simplifying internal connection design. Storage device manufacturers currently invest considerable costs to support different storage devices including Fiber Channel arrays, SATA arrays, etc., and SAS connection technology will be able to pass Use components to reduce design costs. ?
To protect user investment, SAS’s interface technology can be backward compatible with SATA.
The backplane of the SAS system can connect either dual-port, high-performance SAS drives or high-capacity, low-cost SATA drives. In the past, because SCSI and ATA occupied different market segments, and the devices only shared bandwidth, they were incompatible with each other in terms of interfaces, drivers, cables, etc., resulting in the dispersion and isolation of user resources and increasing the total cost of ownership. Now, even if users use different types of hard drives, they do not need to invest again, which is of great significance to the investment protection of enterprise users. However, it should be noted that SATA systems are not SAS compatible, so SAS drives cannot be connected to the SATA backplane. ?
SAS uses expanders that allow more drives to be connected to one or more SAS host controllers. Each expander can have up to 128 physical connections, including other master connections, other SAS expanders, or hard drives. This highly scalable connectivity mechanism enables enterprise-class massive storage space requirements while easily supporting multi-point clustering for automatic failover capabilities or load balancing. Currently, the SAS interface rate is 3Gbps, and most of its SAS expanders are 12 ports. At the same time, 6Gbps or even 12Gbps high-speed interfaces will appear, and 28 or 36-port SAS expanders will appear to adapt to different application needs. Its actual performance is comparable to that of optical fiber.
Since SAS is developed from SCSI, it will be compatible with many manufacturers on the host side. SAS uses a point-to-point connection method. Each SAS port provides 3Gb bandwidth, and the transmission capacity is almost the same as that of 4Gb optical fiber. This transmission method not only improves high reliability and fault tolerance, but also increases the overall performance of the system. On the hard disk side, the switching domain of the SAS protocol can provide 16,384 nodes, while the optical fiber ring can provide up to 126 nodes. The scalability embodied by being compatible with SATA hard drives is another significant advantage of SAS. For different business application scopes, users can flexibly choose different storage media on the hard drive side, reducing user costs as needed. ?
While the SAS interface enjoys various unique advantages, the cost of SAS products starting from the chip level is far lower than that of FC. It is precisely because of the outstanding cost-effective advantage of SAS that SAS has become the most popular in hard disk interfaces. field, posing a great threat to optical fiber storage.