From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Subject: Re: What's the "prepare_discard_fn" supposed to do? Date: Fri, 10 Oct 2008 06:58:53 -0600 Message-ID: <20081010125853.GE25780@parisc-linux.org> References: <1222955524.3518.400.camel@macbook.infradead.org> <48E5C047.7020004@yandex.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Woodhouse , Chris Worley , linux-fsdevel@vger.kernel.org To: Artem Bityutskiy Return-path: Received: from palinux.external.hp.com ([192.25.206.14]:49863 "EHLO mail.parisc-linux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756010AbYJJM6y (ORCPT ); Fri, 10 Oct 2008 08:58:54 -0400 Content-Disposition: inline In-Reply-To: <48E5C047.7020004@yandex.ru> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Fri, Oct 03, 2008 at 09:48:39AM +0300, Artem Bityutskiy wrote: > Sorry for my ignorance, but why "discard" is used in hard drive? What > may it improve? I've always been thinking it is only useful for SSD and > other FTL-enabled beasts. If you look at the work being done in T10, it's also envisaged as being useful for large storage arrays where you do "thin provisioning" -- eg pretend that twenty clients each have a terabyte of disc and only buy five terabytes of disc for the array. When they start to use four terabytes, you'll buy some more discs for it, and nobody will ever know. In order to make this work well, you have to know when files really have been deleted. -- 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."