From: Theodore Tso Subject: Re: Is TRIM/DISCARD going to be a performance problem? Date: Mon, 11 May 2009 10:50:59 -0400 Message-ID: <20090511145059.GD6277@mit.edu> References: <20090510165259.GA31850@logfs.org> <20090511083754.GA29082@mit.edu> <20090511100624.GB6585@logfs.org> <20090511112729.GD29082@mit.edu> <20090511120936.GB6277@mit.edu> <87f94c370905110610j2f5ea7fcua4e596b2b5e82a5f@mail.gmail.com> <20090511142740.GC6277@mit.edu> <4A08365F.5040805@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Greg Freemyer , =?iso-8859-1?Q?J=F6rn?= Engel , Matthew Wilcox , Jens Axboe , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, Linux RAID To: Ric Wheeler Return-path: Content-Disposition: inline In-Reply-To: <4A08365F.5040805@redhat.com> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Mon, May 11, 2009 at 10:29:51AM -0400, Ric Wheeler wrote: > > The key is not at the FS layer - this is an issue for people who RAID > these beasts together and want to actually check that the bits are what > they should be (say doing a checksum validity check for a stripe). > Good point, yes I can see why they need that. In that case, the storage device can't just silently truncate a TRIM request; it would have to expose to the OS its alignment requirements. The risk though is that more they try push this compleixity into the OS, the higher the risk that the OS will simply decide not to take advantage of the functionality. Of course, there is the question why anyone would want to build a software-raid device on top of a thin-provisioned hardware storage unit. :-) - Ted