Machine is an early 2008 Mac Pro. I'm connecting two external SATA desktop hard drives via eSATA (NewerTech Voyager S2 enclosures) and a Newer Technology eSATA Extender Cable (connected to the 5th and 6th internal SATA headers). One of the drives is used as a Time Machine backup disk. This TM disk has been periodically disconnecting and generating warning messages about improper ejection. It reconnects with a restart, but usually will disconnect again within a day. I swapped the drives in the docks, so each was connected via the other dock, cable, and internal header. The same problem persists - the TM disk disconnects periodically despite having switched docks. Seems like it might be a disk problem. Any thoughts? Any way to test for detectable problems?