Re: Question about Request Sense case in scsi_lib.c

[Dave Olien <dmo@osdl.org>]

Tim,

Thanks for the feedback.  Yes, Automatic volume transfer is on, and I
was expecting there'd be poor performance as a result.  I just
didn't expect to get IO errors.  The odd thing is that the "bus reset"
leads to the SCSI request being requeued.  But every once in a while,
the requeue fails with errors and the request is failed.  I'll look at
these cases a little more closely, try to understand why the requeues fail.

I think the dm multipathing software will soon have hooks to
support manual volume transfer in these situations.

Dave

On Tue, Oct 12, 2004 at 09:29:30AM -0700, Tim Pepper wrote:
> I thought on FAStT's while there are dual-active controllers, for a
> given lun they weren't active-active, but rather active-passive with
> either manual or automatic volume transfer.  Assuming automatic volume
> transfer is on and you send IOs to both controllers simultaneously you
> would ping-pong the cache, drive IO rates lower and possibly see that
> manifest itself in interesting behaviour in the linux scsi stack. 
> With manual volume transfer you should get IO errors from the
> controller which is not active or preferred for the given lun.  Maybe
> somebody involved with their RDAC multipathing driver follows this
> list and can comment on their intentions for the 2.6 kernel and dm
> multipathing.