From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Bryn M. Reeves" Subject: Re: [dm-devel] [PATCH 1/1] block: rework flush sequencing for blk-mq Date: Mon, 17 Mar 2014 11:55:18 +0000 Message-ID: <5326E2A6.4080405@redhat.com> References: <20140130132630.GB6031@infradead.org> <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=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140314141301.GA13112@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: device-mapper development Cc: Mike Snitzer , Christoph Hellwig , Jens Axboe , Shaohua Li , "linux-kernel@vger.kernel.org" , Jeff Moyer List-Id: dm-devel.ids On 03/14/2014 02:13 PM, Mike Snitzer wrote: > 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? Do you have find_multipaths set in multipath.conf? It defaults to off. If it's enabled then multipath will only create maps for WWIDs it already knows about (listed in /etc/multipath/wwids) unless there are at least two devices with the same WWID or the user forces the operation: Mar 17 12:26:50 | checking if sdm should be multipathed Mar 17 12:26:50 | wwid 35333333000000000 not in wwids file, skipping sdm Turn it off and multipath will happily map a single path scsi_debug for me: # multipath create: mpathg (35333333000000000) undef Linux,scsi_debug size=1.0G features='0' hwhandler='0' wp=undef `-+- policy='round-robin 0' prio=1 status=undef `- 8:0:0:0 sdm 8:192 undef ready running Iirc this is enabled on at least some current distros by default to avoid creating maps for USB keys and the like. Regards, Bryn.