From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Reinecke Subject: Re: Status of SCSI referrals support in dm-multipath Date: Mon, 02 Jun 2014 08:34:50 +0200 Message-ID: <538C1B0A.6080808@suse.de> References: <20140601224650.000043de@localhost> 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: In-Reply-To: <20140601224650.000043de@localhost> 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: Sebastian Herbszt List-Id: dm-devel.ids On 06/01/2014 10:46 PM, Sebastian Herbszt wrote: > Hello, > > I am trying to find out the status of SCSI referrals support in dm-multip= ath. > SCSI referrals support was a topic at LSF [1] but I wasn't able to find a= ny > information. Back in 2010 Hannes suggested the use of multiple entries in= a > multipath table [2] but this doesn't seem to work (anymore): > > [ 7750.354190] device-mapper: table: Request-based dm doesn't support mul= tiple targets yet > > Is there any SCSI referrals support yet? > > [1] http://marc.info/?l=3Dlinux-scsi&m=3D129553880112460&w=3D2 > [2] http://www.redhat.com/archives/dm-devel/2010-June/msg00155.html > Not as of now. I've managed to push referrals support into = target_core, so you now can set up a backend which supports referrals. And for the multiple entries I've though to use a linear target on = top of the multipath target. The linear target would just split up the device in chunks, = according to the referrals layout. And then you would have several multipath devices (all referring to = the same disk), one for each supported referrals ALUA configuration. The linear target would then map each chunk to the correct multipath = device. It'll be a beast for failover, but should be possible. And maybe it's better to use dm-switch here; the number or referrals = might overflow dm-linear ... 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)