When buying an array or server for storing information, we stop at the choice: what kind of hard drives to install. The most popular types of hard drives are: SAS, SATA, and NL-SAS. These three types belong to the fastest storage media, they store most of the data in the world. Our article is about the first type. We will consider what SAS disks are, what are their parameters, and what is the difference between the main types of devices mentioned.
Specifications
SAS drives replaced the SCSI type. They have become the new standard in enterprise-class information storage. Of the three types listed, SAS disks are considered the most reliable, they are able to maintain performance in very difficult operating conditions. SAS Hard Drives work much better than hard drives like NL or SATA. An indicator of their reliability is such a parameter as the error rate. It determines the probability with which one bit of error can occur in media data. The error rate for SAS-type drives is usually one out of 10 16 bits. That is, this means that the probability of error can occur in one of ten quadrillion bits. For example, you can compare this indicator with the error value in SATA-type hard drives, where it is one out of 10 15 (or one quadrillion). As you can see, the protection of SATA hard drives is also quite high, however, when the question arises about the protection of stored information, the difference is one order of magnitude very significant.
SAS disks are manufactured adhering to more stringent standards than when developing other types of hard drives. So, 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 parameters listed, controllers and drives of the type in question have many additional commands for diagnostics. These features make this technology more efficient than SATA. This is especially evident in force majeure situations.
NL Winchesters
This technology is the "new player" in the market. NL-drives are a hybrid: SATA-hard drive with a connector type SAS. That is, the speed, filling and head are taken from SATA technology, and the interface is fully compatible with SAS. NL technology is inferior to the disks in performance (due to the relatively low speed). However, it is fully consistent with them in the order of commands, as well as multi-threaded data transfer and support for multiple hosts.
Tagged order of sending commands and multi-threaded transmission
The simultaneous coordination of several sets of storage instructions, as well as the information ordered by the storage controller, is transmitted most efficiently. SAS technology provides several full-duplex data transmission channels that provide quick access to stored information. One SAS-type hard drive can be controlled simultaneously from several personal computers without the use of switches.
Conclusion
In essence, SAS and SATA technologies are designed for various purposes: the first for fault tolerance and performance, and the second for capacity. Therefore, they should not compete with each other.