I'm unsure about the differences in these storage interfaces. My Dell servers all have SAS RAID controllers in them and they seem to be cross-compatible to an extent.

The Ultra-320 SCSI RAID controllers in my old servers were simple enough: One type of interface (SCA) with special drives with special controllers, humming at 10-15K RPM. But these SAS/SATA drives seem like the drives I have in my desktop, only more expensive. Also my old SCSI controllers have their own battery backup and DDR buffer - neither of these things are present on the SAS controllers. What's up with that?

"Enterprise" SATA drives are compatible with my SAS RAID controller, but I'd like to know what advantage SAS drives have over SATA drives as they seem to have similar specs (but one is a lot cheaper).

Also, how do SSDs fit into this? I remember when RAID controllers required HDDs to spin at the same rate (as if the controller card supplanted the controller in the drive) - so how does that work out now?

And what's the deal with Near-line SATA?

I apologise about the rambling tone in this message, it's 5am and I haven't slept much.