Using SATA drives with SAS shared backplane

My two cents: If you are concerned about the edge case failures that may occur with SATA hardware (specifically, lousy SATA controllers), spend the money on real SAS disks.

These cards do what they say on the tin: They translate SAS (SCSI) commands to SATA commands, and even implement a few themselves (like power- and spinup-control).
They do nothing else (the drives are still SATA, their performance characteristics are unchanged, their reliability is unchanged, etc.), and they add a new layer of complexity into your environment (They are hardware + software, either of which could fail, have a defect, etc.) -- From my point of view you are increasing your net chance of a failure versus just buying an appropriate SAS drive.

SATA and SAS are point-to-point links. So the total distance is irrelevant, only the link lengths.

The SAS Protocol is used to connect to SAS devices. SATA is used to talk to SATA devices. SAS HBAs and Active Backplanes (aka SAS Expanders) must be able to speak SATA, so it can communicate to SATA drives; and this SATA connection is sent back over the SAS backhauls via the SATA Tunneling Protocol.

I haven't checked the specs yet, but it's likely that the expanders are SAS 1.0 or 1.1 and don't support 6Gb SATA (they would only support 1.5Gb SATA). I have further seen issues with these "older" generation SuperMicro Expanders when using SATA disks the whole chip slows to 1.5Gb instead of just the one lane. This would mean you could only get 1.5Gbx4 to all the drives in the rear of the chassis, and only under ideal conditions.