From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Subject: Re: thin provisioned LUN support & file system allocation policy Date: Fri, 7 Nov 2008 08:45:50 -0700 Message-ID: <20081107154550.GH15439@parisc-linux.org> References: <1225984628.4703.80.camel@localhost.localdomain> <20081107120534.GO21867@kernel.dk> <49143142.4010809@redhat.com> <20081107121934.GP21867@kernel.dk> <49145029.4040900@redhat.com> <20081107144311.GE9543@mit.edu> <4914568A.7090307@redhat.com> <49145E0C.4030705@hp.com> <20081107153624.GG9543@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: Theodore Tso , jim owens , Ric Wheeler , Jens Axboe , Chris Mason , Dave Chinner Received: from palinux.external.hp.com ([192.25.206.14]:38536 "EHLO mail.parisc-linux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750986AbYKGPpw (ORCPT ); Fri, 7 Nov 2008 10:45:52 -0500 Content-Disposition: inline In-Reply-To: <20081107153624.GG9543@mit.edu> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Fri, Nov 07, 2008 at 10:36:24AM -0500, Theodore Tso wrote: > The discussion here has been around Intel-style SSD's, which > apparently have a log-structured filesystem in the device, such that > wear leveling is done automatically, and in fact it is *better* for > these devices if we reuse the same block since then the SSD > automatically knows that contents at the old location is logically > "gone". (I don't believe, or at least don't see, why there would be > any benefit of reusing block ranges versus explicitly using a TRIM > command to tell the SSD that the old block was no longer being used; > it should have the same effect as far as the SSD is concerned.) > > The one thing which I am somewhat concerned about is whether all SSD's > will be doing things the Intel way, or whether other SSD's might not Given that most of my information about how SSDs work comes from a presentation given by Samsung at the FS/IO storage workshop, I feel fairly confident all the manufacturers do something very similar with a log-structured FS internally. Of course, this probably doesn't apply to the $5 1Gb USB keys that you get in the conference schwag, but if we start optimising for those, we've probably already lost. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step."