From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Martin K. Petersen" Subject: Re: [dm-devel] [LSF/MM ATTEND] discuss blk-mq related to DM-multipath and status of XCOPY Date: Wed, 07 Jan 2015 18:39:41 -0500 Message-ID: References: <54AA90B1.1030201@suse.de> <54ACEF13.7000508@suse.de> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <54ACEF13.7000508@suse.de> (Hannes Reinecke's message of "Wed, 07 Jan 2015 09:32:19 +0100") Sender: linux-scsi-owner@vger.kernel.org To: Hannes Reinecke Cc: "Martin K. Petersen" , device-mapper development , Christoph Hellwig , "linux-scsi@vger.kernel.org" List-Id: dm-devel.ids >>>>> "Hannes" == Hannes Reinecke writes: Hannes> Not quite. XCOPY is optional, and the system works well without Hannes> it. So the exception handling would need to copy things by hand Hannes> to avoid regressions. Or defer to user space. But it's really no different from how we do WRITE SAME which may or may not work. If it fails we fall back to writing zeroes. Hannes> Plus XCOPY requires some elaborate setup, and even if those Hannes> succeeded the array might still fail the command. _And_ there Hannes> is no guarantee that that the XCOPY command is actually faster Hannes> than the manual procedure. It saves the data a roundtrip on the fabric. That itself may be more valuable than a direct bandwidth win if there is concurrent I/O on the wire. -- Martin K. Petersen Oracle Linux Engineering