[dm-devel] Re: [PATCH RFC] move scsi parts of dm hw handlers to scsi layer
Philip R. Auld
pauld at egenera.com
Fri Jul 21 12:57:47 UTC 2006
Rumor has it that on Fri, Jul 21, 2006 at 01:41:28PM +0200 Hannes Reinecke said:
> IIRC this is
>
> 'DGC' 'DISK'
> 'DGC' 'RAID 10'
> 'DGC' 'RAID 5'
>
> Hrmph. There is one bit which doesn't quite work out.
> While the hardware handler knows how to handle error codes and how to
> switch
> paths for a specific device, it doesn't know _when_ to switch it.
> I don't think it's a clever idea to switch paths whenever you encounter
> an
> passive path. Seems like you could do a nice ping-pong that way ...
Yes. I agree that having the handlers in SCSI is a better place for
them. However, the architectural decision to have multipath knowledge
at a higher level makes that harder. Some sort of interface into
the scsi layer handlers from the dm/block layer would be more needed.
That way dm or some piece that has the knowledge of the multipath
situation can trigger the failover.
There will still be a need to bubble up information from the decoded
error codes so higher layers can make the correct decision.
Such an interface would need to be in both directions.
Cheers,
Phil
>
> Cheers,
>
> Hannes
>
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--
Philip R. Auld, Ph.D. Egenera, Inc.
Software Architect 165 Forest St.
(508) 858-2628 Marlboro, MA 01752
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