Hello. Given that additional data, I'd say that the scsi layer is
issuing a command the raid devices don't like, and then somehow never
timing out and re-issuing the command to wake up the raid devices again.
I'll bet if you put each raid device on a separate channel of a
dual-channel scsi card, you don't see the problem either, right?
Once the problem manifests, can you get things going again with a scsictl
/dev/sdx reset?
If so, then I'd say that our scsi stack is doing something to foobar the
raid devices, or the raid devices themselves are not complying with the
scsi standard somewhere. In other words, I'd characterize this is a badly
behaved device/disk.
-Brian