Re: [dm-devel] [LSF/MM ATTEND] discuss blk-mq related to DM-multipath and status of XCOPY

[Hannes Reinecke <hare@suse.de>]

On 01/07/2015 12:55 AM, Martin K. Petersen wrote:
>>>>>> "Hannes" == Hannes Reinecke <hare@suse.de> writes:
> 
> Hannes> Yep. That definitely needs to be discussed.  Especially we'd
> Hannes> need to discuss how to handle exceptions, seeing that XCOPY
> Hannes> might fail basically at any time.  
> 
> Like any SCSI command :)
> 
Not quite. XCOPY is optional, and the system works well without it.
So the exception handling would need to copy things by hand to avoid
regressions.

Plus XCOPY requires some elaborate setup, and even if those succeeded
the array might still fail the command.
_And_ there is no guarantee that that the XCOPY command is actually
faster than the manual procedure.

I guess we'll need some timing / initialisation routine to figure
out what speed-up is to be had with XCOPY.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
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