SAS-drives: purpose, description, technical characteristics of the device

Buying an array or server for storagewe stop before the choice: what kind of hard drives to install. The most popular are the following types of hard drives: SAS, SATA and NL-SAS. These three types are among the fastest data carriers, they store most of the data in the world. Our article is devoted to the first type. We will look at what SAS drives are, what their parameters are, and what is the difference between the basic types of these devices.

Specifications

SAS-disks replaced the SCSI-type. They have become a new standard in storing corporate-class information. Of the three listed types, SAS drives are considered the most reliable, they are able to support performance in very difficult operating conditions. SAS Hard Drives work much better than NL orSATA. The indicator of their reliability is a parameter such as the error rate. It determines the probability with which one error bit can occur in media data. The error rate for SAS hard drives is usually one of 10¹⁶bit. That is, it means that the probability of error can occur in one of ten quadrillion bits. For example, you can compare this with the value of the error in hard disks such as SATA, where it is a unit of 10¹⁵ (or one quadrillion). As you can see, the protection of SATA-hard drives is also quite high, however, when the question arises of protecting the stored information, the difference by one order is very significant.

SAS-drives are produced by adhering to more strictstandards than with the development of other types of hard drives. Thus, this technology is characterized by an average time between failures of 1.6 million hours, and SATA technology - 1.2 million. In addition to the listed parameters, controllers and disks of the type in question have many additional commands intended for diagnostics. These functions make this technology more efficient than SATA. This is especially evident in force majeure situations.

NL Winchesters

This technology is a "new player" in the market. NL-drives are a hybrid: a SATA hard drive with a SAS connector. That is, the speed, fill and head are taken from SATA-technology, and the interface is fully compatible with SAS. NL technology is inferior to the drives in question in performance (due to the relatively low rotation speed). However, it fully corresponds to them in the order of the commands, as well as multithreaded data transmission and support of several hosts.

Tagged order of sending commands and multithreaded transmission

Simultaneous coordination of several setsstorage instructions, as well as information ordered by the storage controller, is transmitted most effectively. The SAS technology provides several full-duplex data links that provide quick access to the stored information. One SAS-type hard drive can be controlled from several personal computers without the use of switches.

Conclusion

In fact, SAS and SATA technologies are designed fordifferent purposes: the first for fault tolerance and performance, and the second - to provide capacity. Therefore, they should not compete with each other.