Comment # 7 on bug 1018839 from Keith Busch

There's a couple different issues here. The status '6' on the "set queue count"
is an internal device error and indicates the controller is in some degraded
mode incapable of issuing IO.

In other log snippets here, it says the IO is timing out. That's not a good
thing either. In most cases, the driver has to forcefully end the IO, which you
see with the negative status codes (fffffffc). In other cases, it looks like
the drive did return a completion when the status is 000. In either case,
though, we should expect the drive return completions timely, and it looks like
your timeout value is set to 30 seconds, so that should be more than
reasonable.