From: Jeff Layton Subject: Re: Client performance questions Date: Mon, 10 Dec 2007 18:26:11 -0500 Message-ID: <20071210182611.56cdc01b@tleilax.poochiereds.net> References: <0a15723c4b267d4eb8b5ad05800315c0@swip.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Cc: "linux-nfs@vger.kernel.org" To: "Fredrik Lindgren" Return-path: Received: from mx1.redhat.com ([66.187.233.31]:37985 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751798AbXLJX0R (ORCPT ); Mon, 10 Dec 2007 18:26:17 -0500 In-Reply-To: <0a15723c4b267d4eb8b5ad05800315c0-FpffG6+3qsA@public.gmane.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Mon, 10 Dec 2007 22:52:51 +0100 "Fredrik Lindgren" wrote: > Hello > > We have a mail-application running on a set of Linux machines using > NFS for the storage. Recently iowait on the machines has started to > become a problem, and it seems that they can't quite keep up. Iowait > figures of 50% or above are not uncommon during peak hours. > High iowait numbers are not a problem in and of themselves. A high iowait number is just indicative that the machine is spending a lot of its time waiting for I/O. On a busy NFS client, that may be expected particularly if the machine isn't doing much else CPU-wise. The big question is whether you're getting enough throughput for your applications. iowait percentages can't tell you that. That's not to say that you don't have a performance issue, but you'll probably need to get some better metrics than iowait figures to track it down. -- Jeff Layton