Investigate your SAN performance. We have experienced this exact situation on a Virtualized SQL Server where it appeared that Data, Log, TempDb and Backups were on separate LUNs, but the associated virtual disks (VMDKs) had all been placed on a single VMWare DataStore, which was actually a single LUN presented from the SAN, due to usage of EMC Storage Pools. All IO was actually going thru 1 path at VMWare Host level. Every time we'd get the OS 170 Error, without associated Disk Errors in the System Event Log (suspect due to disk.sys timeout values Registry being increased by VMWare vSCSI drivers). Fix was Storage vMotion to faster Storage Pool on SAN. (Still not happy with single DataStore though!)