[dm-devel] RE: SCSI Hardware Handler and slow failover with large number of LUNS

[Chandra Seetharaman]

On Mon, 2009-04-06 at 11:38 -0400, berthiaume_wayne at emc.com wrote:
> Hi Chandra.
> 
> 	We're currently testing 1024 LUNs across four paths with the
> older handler but will be doing the same with the new handler later this

Hi Wayne,

What do you mean by "older" handler ? dm_emc ?

> month. It sounds like I should move this up in the queue. 
> 
> Regards,
> Wayne. 
> 
> -----Original Message-----
> From: linux-scsi-owner at vger.kernel.org
> [mailto:linux-scsi-owner at vger.kernel.org] On Behalf Of Chandra
> Seetharaman
> Sent: Saturday, April 04, 2009 5:31 PM
> To: dm-devel; Linux SCSI Mailing list
> Cc: Moger, Babu
> Subject: SCSI Hardware Handler and slow failover with large number of
> LUNS
> 
> Hello All,
> 
> During testing with the latest SCSI DH Handler on a rdac storage, Babu
> found that the failover time with 100+ luns takes about 15 minutes,
> which is not good.
> 
> We found that the problem is due to the fact that we serialize activate
> in dm on the work queue.
> 
> We can solve the problem in rdac handler in 2 ways
>  1. batch up the activates (mode_selects) and send few of them.
>  2. Do mode selects in async mode.
> 
> Just wondering if anybody had seen the same problem in other storages
> (EMC, HP and Alua). 
> 
> Please share your experiences, so we can come up with a solution that
> works for all hardware handlers.
> 
> regards,
> 
> chandra
> 
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