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 10:42:09 -0400 Message-ID: <4A8D60C1.6000809@redhat.com> References: <20090816004705.GA7347@infradead.org> <20090819203916.GA25296@elte.hu> <4A8CA956.2060406@rtr.ca> <4A8D5442.1000302@redhat.com> <4A8D5FDB.7080505@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: In-Reply-To: <4A8D5FDB.7080505@rtr.ca> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On 08/20/2009 10:38 AM, Mark Lord wrote: > Ric Wheeler wrote: >> >> 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... > .. > > Well, that's a bit drastic. But the RAID software should at least > not issue TRIM commands in ignorance of such. If the storage can return different data in a sequence of READ requests of the same sector (with no writes), there is nothing RAID could do. It would see total garbage... > Would it still be okay to do the TRIMs when the entire parity stripe > (across all members) is being discarded? (As opposed to just partial > data there being dropped) This should be safe if the MD bitmaps would prevent us from trying to READ/regenerate parity for that stripe... ric