From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ric Wheeler Subject: Re: [PATCH, RFC] xfs: batched discard support Date: Thu, 20 Aug 2009 09:48:50 -0400 Message-ID: <4A8D5442.1000302@redhat.com> References: <20090816004705.GA7347@infradead.org> <20090819203916.GA25296@elte.hu> <4A8CA956.2060406@rtr.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Ingo Molnar , Christoph Hellwig , Peter Zijlstra , Paul Mackerras , Linus Torvalds , xfs@oss.sgi.com, linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, jens.axboe@oracle.com, IDE/ATA development list , Neil Brown To: Mark Lord Return-path: Received: from mx1.redhat.com ([209.132.183.28]:32896 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754335AbZHTNuc (ORCPT ); Thu, 20 Aug 2009 09:50:32 -0400 In-Reply-To: <4A8CA956.2060406@rtr.ca> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On 08/19/2009 09:39 PM, Mark Lord wrote: > [resending, after fixing the Cc: list; somebody trimmed it earlier] > > Jamie Lokier wrote: > .. >> I don't remember - does TRIM guarantee the blocks read zeros afterwards? > .. > > No, it doesn't. > > A drive can optionally support "deterministic TRIM", whereby it will > return > consistent data for any given trimmed sector afterwards, but that > doesn't mean zeros. > > -ml Note that returning consistent data is critical for devices that are used in a RAID group since you will need each RAID block that is used to compute the parity to continue to return the same data until you overwrite it with new data :-) If we have a device that does not support this (or is misconfigured not to do this), we should not use those devices in an MD group & do discard against it... ric