With Seagate’s latest Constellation and Constellation ES HDD families, the drives are offered in both 6Gb SAS or 6Gb SATA versions. Both drive families are enterprise-class, so it begs the question: “Why are there models available using the desktop-oriented SATA interface in the first place? And with the option of both interfaces, which do you choose?”
If we were making the choice going strictly by features, it’d be a no-brainer — SAS definitely does have a more diverse and advanced feature set. At a very high level, this includes the ability for SAS to 1) support multiple initiators over the SAS domain, 2) deliver advanced error-recovery and reporting, and 3) support cable lengths up to 10 meters in length.
With that said, SAS is clearly made for enterprise systems where the ability to scale out large numbers of drives, as well as making sure that data is error-free and correctable, are key attributes. SATA on the other hand was made for desktop PCs with its simpler capabilities.
So to rephrase our original question: “Why SATA for anything?”
Well, it costs a little less, for one — but what kinds of systems might do well without SAS? The answer can be found in the application and workload. For years, smaller servers, used for small-to-medium-sized businesses (SMBs), have been built around the use of lower-cost desktop SATA (or parallel ATA before that) HDDs. While this was o.k. if the server’s workload remained low, some of these organizations were pushing the limits of those servers with client machines hitting them for information continuously. The result was sometimes premature HDD failure, since desktop-class drives weren’t designed for data-intensive or 24×7 operation in the first place.
The SATA versions of Constellation ES (3.5-inch form factor) are a good fit for those environments where organizations want to keep their current SATA-based system, but upgrade to a more robust HDD. Or if an organization knows that its needs are for a small storage system, and future scaling isn’t a concern, a SATA system using the Constellation ES or the 2.5-inch small form factor Constellation will do well.
However, for organizations keen on keeping an eye on the need for expansion of server or storage performance and capacity, building a system based around a SAS infrastructure is the way to go.