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

[berthiaume_wayne at emc.com]

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
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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