SATA, SAS and NL-SAS disks
There are different kinds of hard drives: Serial Attached SCSI (SAS), Near Line SAS (NL-SAS), Serial ATA (SATA), Fiber channel (FC) and Solid State Drives (SSD). FC and SSD are fast and faster disks. Let’s see about the first three. So, what is the real difference between SAS, NL-SAS and SATA disks?
Of the three kinds of disks we are discussing about, this is the most reliable and maintains its performance under more difficult conditions.
- The BER (bit error rate) is generally 1 in 10^16 bits – how often bit errors may occur on the media
- Mean time between failure of 1.6 million hours
- Supports command queuing. Simultaneously coordinates multiple sets of storage instructions by reordering them at the storage controller level so that they’re delivered to the disk in an efficient way.
- Concurrent data channels. SAS includes multiple full-duplex data channels, which provides for faster throughout of data.
- Multiple host support. A single SAS disk can be controlled by multiple hosts without need of an expander.
SATA is the slowest disk that we use on servers and storage these days. It is used for low-tier or mass storage needs where the capacity and cost matter more than the performance and reliability. It does not have the enterprise benefits of SAS, like Command Queuing, Concurrent Data Channels, etc..,
Near Line SAS is basically a merging of SATA disk with SAS interface / controller. It’s performance is close to SATA.
An NL-SAS disk is a bunch of spinning SATA platters with the native command set of SAS. While these disks will never perform as well as SAS thanks to their lower rotational rate, they do provide all of the enterprise features that come with SAS, including enterprise command queuing, concurrent data channels, and multiple host support.
Command Queuing / NCQ (Native) explained: