If you provision storage for modular systems that can interchangeably accept both SATA and SAS drives, you’ll soon see a dizzying series of options that may make administrators confused. Many drive manufacturers are offering 2TB SAS drives. Yes, that is 2TB SAS. Of course, there is more to it than what it may seem.

My issue with this is that administrators may confuse a SAS drive as better without looking at the details, so I’m trying to ensure that everyone understands the difference in these configurations. In the simplest of configurations, SAS drives may be marked as a “tier 1” storage and SATA as a “tier 2″offering in servers and storage area networks. The traditional SAS drive marketed as an enterprise offering rotates at 15,000 RPM or higher and currently we see 600GB as the largest offering.

I’ve specifically noticed Oracle and HP offering the 2TB SAS drive. The Oracle offering first showed up to me on the Oracle Unified Storage System product line with 2TB SAS drives, and I was a little taken back by this at first. Now, HP is offering 2TB SAS drives that are not much different in price than their 2TB SATA drive. The secret here is that the inner workings of the SAS and comparable SATA drives are effectively the same; the only difference is the bus interface. So, be careful reading specifications that will document a 2TB SAS drive running at 7200 rpm can transfer data at 75 GBps.

The SAS bus can do that, but these drives can’t transfer at that rate. The 2TB SATA drive has a transfer rate of 300 MBps, which I think is more realistic for the SAS version as well. Further, HP’s web site does a good job in spelling out the cost differences between the two models. The SAS version has an MSRP of $949 and SATA version has an MSRP of $899. I’d happily pay the extra $50 for that type of throughput differential, if it were possible.

Of course we should see the good side of this, and that is backplane consistency. The slower drives with a SAS interface can be utilized to ensure a consistent drive type on an array, or if the array doesn’t support SATA drives; the use case can be made for the 2TB SAS drives.

Make no mistake; I’ll still buy the 2TB SAS drive (knowing that it is effectively a SATA drive) for configurations where they are interchangeable. Have you come across this potentially confusing disk configuration? If so, share your comments below.