From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Tokarev Subject: Re: linear writes to raid5 Date: Tue, 18 Apr 2006 18:28:56 +0400 Message-ID: <4444F7A8.7050304@tls.msk.ru> References: <17465.43983.345817.253532@cse.unsw.edu.au> <17468.18087.901186.523228@cse.unsw.edu.au> <17474.53696.831154.37427@cse.unsw.edu.au> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <17474.53696.831154.37427@cse.unsw.edu.au> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: Alex Tomas , linux-raid@vger.kernel.org List-Id: linux-raid.ids Neil Brown wrote: [] > raid5 shouldn't need to merge small requests into large requests. > That is what the 'elevator' or io_scheduler algorithms are for. There > already merge multiple bio's into larger 'requests'. If they aren't > doing that, then something needs to be fixed. > > It is certainly possible that raid5 is doing something wrong that > makes merging harder - maybe sending bios in the wrong order, or > sending them with unfortunate timing. And if that is the case it > certainly makes sense to fix it. > But I really don't see that raid5 should be merging requests together > - that is for a lower-level to do. Hmm. So where's the elevator level - before raid level (between e.g. a filesystem and md), or after it (between md and physical devices) ? I mean, mergeing bios into larger requests makes alot of sense between a filesystem and md levels, but it makes alot less sense to do that between md and physical (fsvo "physical" anyway) disks. Thanks. /mjt