From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ric Wheeler Subject: Re: RFC: use TRIM data from filesystems to speed up array rebuild? Date: Tue, 04 Sep 2012 18:59:33 -0400 Message-ID: <504687D5.4020302@gmail.com> References: <50464322.3010509@genband.com> <5046525E.10500@gmail.com> <20120905062405.3741239a@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120905062405.3741239a@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: NeilBrown Cc: Chris Friesen , linux-raid@vger.kernel.org, Joe Thornber , device-mapper development List-Id: linux-raid.ids On 09/04/2012 04:24 PM, NeilBrown wrote: > On Tue, 04 Sep 2012 15:11:26 -0400 Ric Wheeler wrote: > >> On 09/04/2012 02:06 PM, Chris Friesen wrote: >>> Hi, >>> >>> I'm not really a filesystem guy so this may be a really dumb question. >>> >>> We currently have an issue where we have a ~1TB RAID1 array that is mostly >>> given over to LVM. If we swap one of the disks it will rebuild everything, >>> even though we may only be using a small fraction of the space. >>> >>> This got me thinking. Has anyone given thought to using the TRIM information >>> from filesystems to allow the RAID code to maintain a bitmask of used disk >>> blocks and only sync the ones that are actually used? >>> >>> Presumably this bitmask would itself need to be stored on the disk. >>> >>> Thanks, >>> Chris >>> >> Device mapper has a "thin" target now that tracks blocks that are allocated or >> free (and works with discard). >> >> That might be a basis for doing an focused RAID rebuild, > I wonder how.... > Maybe the block-later interface could grow something equivalent to > "SEEK_HOLE" and friends so that the upper level can find "holes" and > "allocated space" in the underlying device. > I wonder if it is time to discard the 'block device' abstraction and just use > files every .... but I seriously doubt it. > > NeilBrown I don't think that we have to go to that extreme, but I think it would be very useful to see if the device mapper people have ideas in how the thin target might be used in combination with MD :) ric