From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: write is faster whan seek? Date: Wed, 11 Jun 2008 13:55:27 +0200 Message-ID: <20080611115524.GX20851@kernel.dk> References: <484FB92D.4090808@hp.com> <20080611114950.GW20851@kernel.dk> <484FBC6B.3080703@hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Dmitri Monakhov , linux-fsdevel@vger.kernel.org To: "Alan D. Brunelle" Return-path: Received: from brick.kernel.dk ([87.55.233.238]:5924 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751048AbYFKLz3 (ORCPT ); Wed, 11 Jun 2008 07:55:29 -0400 Content-Disposition: inline In-Reply-To: <484FBC6B.3080703@hp.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, Jun 11 2008, Alan D. Brunelle wrote: > Jens Axboe wrote: > > On Wed, Jun 11 2008, Alan D. Brunelle wrote: > >> Dmitri Monakhov wrote: > >> > >> Could it be that in the first case you will have merges, thus creating > >> fewer/larger I/O requests? Running iostat -x during the two runs, and > >> watching the output is a good first place to start. > > > > I think it's mostly down to whether a specific drive is good at doing > > 124kb writes + 4k seek (and repeat) compared to regular streaming > > writes. The tested disk was SATA with write back caching, there should > > be no real command overhead gain in those size ranges. > > > > Probably true, I'd think the iostat -x data would be very helpful though. Definitely, the more data the better :). I already asked for blktrace data, that should give us everything we need. -- Jens Axboe