From: Eric Sandeen Subject: Re: Ext4 and xfs problems in dm-thin on allocation and discard Date: Tue, 19 Jun 2012 09:23:33 -0500 Message-ID: <4FE08B65.70303@redhat.com> References: <4FDF9EBE.2030809@shiftmail.org> <20120619141933.GC10637@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: =?UTF-8?B?THVrw6HFoSBDemVybmVy?= , Spelic , xfs@oss.sgi.com, linux-ext4@vger.kernel.org, device-mapper development To: "Ted Ts'o" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:53319 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751301Ab2FSOXs (ORCPT ); Tue, 19 Jun 2012 10:23:48 -0400 In-Reply-To: <20120619141933.GC10637@thunk.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 6/19/12 9:19 AM, Ted Ts'o wrote: > On Tue, Jun 19, 2012 at 04:09:48PM +0200, Luk=C3=A1=C5=A1 Czerner wro= te: >> >> With thin provisioning you'll get totally different file system >> layout than on fully provisioned disk as you push more and more >> writes to your drive. This unfortunately has great impact on >> performance since file systems usually have a lot of optimization on >> where to put data/metadata on the drive and how to read them. >> However in case of thinly provisioned storage those optimization >> would not help. And yes, you just have to expect lower performance >> with dm-thin from the file system on top of it. It is not and it >> will never be ideal solution for workloads where you expect the best >> performance. >=20 > One of the things which would be nice to be able to easily set up is = a > configuration where we get the benefits of thin provisioning with > respect to snapshost, but where the underlying block device used by > the file system is contiguous. That is, it would be really useful to > *not* use thin provisioning for the underlying file system, but to us= e > thin provisioned snapshots. That way we only pay the thinp > performance penalty for the snapshots, and not for normal file system > operations. This is something that would be very useful both for ext= 4 > and xfs. I agree, and have asked for exactly the same thing... though I have no idea how hard it is to disentangle allocation-aware snapshots from thin= g provisioned storage. -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html