From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Reinecke Subject: Re: RHEL 5.4 multipath doesn't handle virtio block devices Date: Tue, 30 Mar 2010 09:16:10 +0200 Message-ID: <4BB1A53A.4030806@suse.de> References: <20100330121606.54b4a50c@martins.ozlabs.org> <4BB186F6.1050402@ct.jp.nec.com> <20100330172358.69e794b9@martins.ozlabs.org> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20100330172358.69e794b9@martins.ozlabs.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: device-mapper development Cc: k-ueda@ct.jp.nec.com List-Id: dm-devel.ids Martin Schwenke wrote: > On Tue, 30 Mar 2010 14:07:02 +0900, Kiyoshi Ueda > wrote: > = >> Why do you want to use dm-multipath on virtio block devices? > = > For consistency rather than failover... :-) > = > I'm using virtual machines to test a clustered NAS environment. The > production setup expects to see dm devices from dm-multipath. So I'm > using dm-multipath on virtio block devices to simulate use of > dm-multipath in a SAN environment. = > = megasas megasas megasas ... I posted a megasas HBA emulation for KVM a while back. Would solve your problem rather elegantly. But then you'd have to recompile KVM, at which point you could include the SCSI emulation as well ... > The RHEL 5.4 version of KVM doesn't contain a SCSI emulation, so the > only 2 choices for large numbers of block devices are virtio and > iSCSI. I'm trying to keep my options open for both of these. > = > The fix for virtio block devices seems quite straightforward, so I > thought I would propose it. :-) > = Problem is, though, that you don't have a unique ID for virtio devices. EG scsi_id and friends don't work here. And AFAIR there is no feature flag which would allow you do set one. How do you distinguish between, say, 2 virtio devices across 2 paths? Cheers, Hannes -- = Dr. Hannes Reinecke zSeries & Storage hare@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=FCrnberg GF: Markus Rex, HRB 16746 (AG N=FCrnberg)