An overview of SAS Drives

When you go for a Server or a Storage hard disk array, the first question that hits the mind is what type of hard disk must be included on the platform. In this article we will focus on Serial Attached SCSI (SAS) drives, along with a brief discussion on Near Line SAS (NL-SAS) and Serial ATA or SATA drives.

Serial Attached Small Computer System Interface is a point to point serial protocol that is used to move data from and to hard drives. Those drives which use this protocol are mentioned as SAS drives and are similar in form factor to SATA drives. Apart from the form factor, SAS drives are offered with several high performance advantages like the platter speed.

Unlike, their SATA drive cousins, SAS drives have the ability to operate with platter speeds ranging in between 10K – 15K. However, when Mean Time Before Failure is taken into account, SAS drives MTBF is 1.6million hours (say around 182 years approximately), which is a bit higher than SATA drives, as MTBF of them is just 1.2 million hours (136 years approximately).

SAS drives are usually utilized in environments where 24/7 high end operations are essential and where speed and I/O frequency needs to reign at a supreme level. They can bear 100% workload and have a latency of 5.7 msec at 15,000RPM.

The rotational vibration tolerance of SAS drives is up to 21 rads/sec/sec and is capable to deliver 319 IOPS. SAS drives require 7 to 15 seconds to recover from bad sectors, almost half the time, when compared with the SATA drives. SAS drives can work for 1.2 million hours and can sustain 45 degrees Celsius temperature in the work environment.

End to end data integrity checks are made by SAS drives from time to time. As SAS controllers can support multitude or additional commands, they are more efficient than SATA drives.

These days, NL- SAS drives are the latest craze in storage field and are a mix up of SATA drives with SAS interface. So, NL- SAS drives are a bunch of spinning SATA platters, running on SAS commands. Although, the performance of NL- SAS drives is not like SAS, other features like enterprise command queuing, concurrent data channels and multiple host support are available in these drives.

Enterprise command queuing also known a tagged command lineup is a feature, where simultaneous coordination of multiple sets of storage instructions is possible with the help of storage controller. This makes the command delivered to the disk in an efficient way.

Concurrent data channels- This feature offers faster throughput of data with the support to multiple full duplex data channels.

Multiple Host support- Due to this feature a single SAS disk can be controlled by multiple hosts in the absence of an expander.

On a conclusion note, SAS drives will definitely constitute one side of the storage coin, while the other will be surfaced with SATA drives. In between the two are NL-SAS drives, which bring in the capabilities of SATA drives with SAS interface, but lack SAS drives reliability.


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