SAS vs Near-line SAS vs SATA

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http://serverfault.com – 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" (HowTos)