From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: scsi_debug and mutipath, was Re: [PATCH 1/1] block: rework flush sequencing for blk-mq Date: Sat, 15 Mar 2014 06:28:26 -0700 Message-ID: <20140315132826.GA17752@infradead.org> References: <20140308155240.GA32297@infradead.org> <531B74B6.4070004@suse.de> <20140312102849.GA26509@infradead.org> <20140313161347.GA6598@redhat.com> <20140314092519.GA10139@infradead.org> <20140314130021.GA12589@redhat.com> <20140314132323.GA14606@infradead.org> <20140314141301.GA13112@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20140314141301.GA13112@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Mike Snitzer Cc: Hannes Reinecke , "linux-kernel@vger.kernel.org" , dm-devel@redhat.com, Benjamin Marzinski , Doug Gilbert , linux-scsi@vger.kernel.org List-Id: dm-devel.ids On Fri, Mar 14, 2014 at 10:13:01AM -0400, Mike Snitzer wrote: > I was more reacting to the assertion you made like multipath regresses > all the time. I'm not faulting you at all for not having tested > multipath. Hell, I even forget to test multipath more than I should. > /me says with shame And I didn't assert that, I just asserted that it gets little testing. > Yeah, not sure why single path scsi_debug "just works", maybe it is a > "feature" of the older multipathd I have kicking around?, but for basic > data path testing scsi_debug is a quick means to an end. I can look > closer at _why_ it gets multipathd in a bit. But maybe Ben or Hannes > will have quicker insight? > > For me, if multipathd is running, if I issue the following a multipath > device gets layered ontop of the associated scsi_debug created sd > device: modprobe scsi_debug dev_size_mb=1024 > > I think it useful to have scsi_debug work with multipath. I know people > in Red Hat's QE organization have even simulated multiple paths with > it.. but I don't recall if they had to hack scsi_debug to do that. I'll > try to find out. Looks like it really shouldn't attach as-is. But scsi_debug should be easily extendable to export two LUNs for the same backing store to help multipath testing.