Wandering Thoughts archives


Why people care about SAS despite not being 'enterprise'

The short way to describe SAS (Serial Attached SCSI) is that it's the 'enterprise' version of SATA. This isn't literally the case (SAS evolved from SCSI, while SATA came from ATA), but in practice the two occupy more or less the same niche as disk interconnect technologies. As the Wikipedia page will tell you, there's little physical difference between them (which is good for everyone), and you can often connect to SATA drives using SAS controllers and other hardware.

My workplace is definitely not an enterprise type of place and we certainly don't have the enterprise level of money that you generally need to get into SAS disks. Despite that we have an enduring interest in and involvement with SAS that dates back to our second generation fileservers, and we're probably not the only people. There are two parts to why.

The first part is what I mentioned above, which is that you can talk to SATA drives with SAS controllers. The second part is that good quality multi-port SAS controller cards are reasonably widely available (usually in 8 and 16 port versions) and not too expensive, and you'll even find a certain number of motherboards with onboard SAS controllers. When you put these together, using a SAS controller (or two) is often the easiest way to put together a good quality server with a bunch of disks. If you want 8 or 12 or 16 or 24 or even 32 disks in a server, you can do that with at most two 16-port SAS controller cards.

There's no reason that there couldn't be widely available, good quality multi-port SATA controllers with high-density IPASS (SFF-8087) connectors that would let you connect to up to 8 or 16 SATA drives in a sensible card size with a manageable amount of cables. But pragmatically these don't really exist, so people (us included) buy SAS controller cards and motherboards with SAS controllers, then connect them all to SATA disks to build relatively inexpensive storage servers.

(I suspect that this is partly an issue of historical demand and SAS basically getting there first. It used to be that systems with a lot of disks were definitely 'enterprise', so SAS had a foothold. Now one line of SAS controllers can sell to both the SATA disk people and the SAS disk using enterprise people, which helps with sales volume. The bad old days had SATA port multipliers, but they were a different kind of thing.)

tech/SASWhyWeCare written at 00:14:53; Add Comment

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