In a nutshell, SAS is to servers, what SATA is to desktops. SAS means Serial Attached SCSI, SATA – Serial Advanced Technology Attachment, the new version of the old PC flat ribbon style connector for the PATA, Parallel Advanced Technology Attachment. SAS means a higher price, built like a tank… to last, moderate capacity and much better performance. SATA means built to a price point, much larger capacity, weak performance compared to SAS, built to be thrown away.
The interesting thing is that Google uses, or at least used to use SATA drives which lasted up to five years, with a very high early failure rate and were not very suceptible to temperature flucuations. On the other hand Google uses hundreds of thousands of drives and they use all types of distributed data technology to get the performance level they do, spending fortunes of a variety of techniques. The take on this, is that for Google, drive capacity and overall cost was more important as they had so many drives and data centers to work with. For the enterprise customer they must make do with less, much less.
While you can run SAS in your desktop, its overkill. Why? Because although very, very fast and much faster than SATA drives, they are designed for multiple users to access data simultaneously, are relatively expensive per gigabyte and are more reliable than SATA drives. SATA on the other hand are cheap to buy and are really a commodity, are available in very large capacity, far larger than SAS drives and have reasonable performance for the single user, or a workgroup with just a few people accessing data from it.
So in the data center, or server room you use SAS drives, and the desktop, SATA.
The newer SAS drives spin from 10,000-15,000 rpm, the SATA, 4,500-7,200 and in a few cases, 10,000.