From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Reinecke Subject: multipath and READ_CAPACITY Date: Thu, 24 Jul 2014 10:46:31 +0200 Message-ID: <53D0C7E7.6090806@suse.de> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1"; Format="flowed" Content-Transfer-Encoding: quoted-printable Return-path: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Christophe Varoqui Cc: device-mapper development , Bart Van Assche List-Id: dm-devel.ids Hi Christophe, I've had a customer issue where someone complained that multipath = would reject paths if they are in ALUA 'standby'. As it turns out, SPC-3 does _not_ require the READ_CAPACITY command = to be implemented if a target port is in standby. Consecutively, linux would register this path with a capacity of = '0', and multipath would reject the path in ev_add_path(). Which makes we wonder, do we actually _need_ the check for a matched = capacity? With VPD page 0x83 pretty much standard as of now (and I'm reasonbly = sure we'll reject any device _not_ providing VPD page 0x83 anyway) = we basically have to rely on that information. IE if the WWID is identical we have assume the devices are = identical. So it would make sense to just remove the check altogether. Thoughts? Cheers, Hannes -- = Dr. Hannes Reinecke zSeries & Storage hare@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=FCrnberg GF: J. Hawn, J. Guild, F. Imend=F6rffer, HRB 16746 (AG N=FCrnberg)