Aug 23, 2011

What's the difference between SAS and SATA drives?

We're speccing out a new server and have a choice between SAS drives and SATA drives. I'd like to use SATA because they're cheaper, but I've seen many of our servers are using SAS, which appear to be compatible in some way or another (one server was apparently upgraded from smaller SAS volumes to SATA volumes. 


Any suggestions?


Now there are a number of solutions that allow you to 'tier' your storage.  Meaning you can buy a cost effective mix of SAS, SATA, and SSD and a volume controller can automatically place the data you use the most on the most efficient, fastest disk choice and move the data that is least used to the less expensive slower disk. 


This allows you to add a handful of the really expensive SSDs and get performace/trhoughput that is 20-30% faster.


Coupled with a virtualized environment and a SAN volume controller device you can control multiple independant storage systems with different disks on different vendors equipment running file or block storage across SATA, SAS, or SSD.  Really impressive stuff.  


Why waste time with SAS and SATA if you could just run an SSD instead? Sure it's more expensive, but more reliable and there are no moving parts to go bad over time. Soooo much faster too.


Are you kidding? Enterprise-grade Intel SSD's cost $600 for a 64gb drive; I can pick up a 146gb 15k SAS drive from Dell or HP for a lousy $130. Outfitting an array of non-consumer SSDs is still prohibitively expensive and I don't expect that to change for at least 3 years. Sure SSDs have no moving parts but there's enough money left over from building a 5 drive RAID5 subsystem that I could build additional servers to store offsite for a private cloud backup.


While SATA drives might run in a SAS controller, SAS drives are usually only  used in servers. They're more expensive because they have better error correction and can come in speeds of up to 15,000 RPM, 2x-3x that of most SATA drives (4500-7200 RPM).


SAS drives won't work on a SATA controller because even though the pinouts are similar because of the plastic connecting the 2 groups of connectors - this is missing on SATA drives.

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