From owner-freebsd-questions@FreeBSD.ORG Wed Nov 10 18:33:43 2010 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 39ED41065696 for ; Wed, 10 Nov 2010 18:33:43 +0000 (UTC) (envelope-from chris@smartt.com) Received: from mailout2.smartt.com (mailout2.smartt.com [69.67.187.26]) by mx1.freebsd.org (Postfix) with ESMTP id 2475F8FC18 for ; Wed, 10 Nov 2010 18:33:42 +0000 (UTC) Received: from [69.31.174.220] (chris-workstation.smartt.com [69.31.174.220]) by mailout2.smartt.com (Postfix) with ESMTPA id 5E9EF10E4A0 for ; Wed, 10 Nov 2010 10:14:09 -0800 (PST) Message-ID: <4CDAE141.8000600@smartt.com> Date: Wed, 10 Nov 2010 10:15:29 -0800 From: Chris St Denis User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.12) Gecko/20101027 Thunderbird/3.1.6 MIME-Version: 1.0 To: freebsd-questions@freebsd.org Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: UFS Snapshots and iowait X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 10 Nov 2010 18:33:43 -0000 I have started using "mount -u -o snapshot" as part of my backup process in order to have a week worth of local differential backups to allow quick and easy recovery of lost/overwritten/etc files. The snapshot of the partition (~250G and 2.3 million inodes used. ~10GB of data change per day) takes around 10 minutes to complete. During the first 5 minutes everything seems to be find, but during the second 5 minutes the Apache processes that are logging to this drive start building up in L (logging) state until they hit MaxClients. Is this just due to the very high io bandwidth usage associated with making a snapshot, or does the creation of this snapshot completely block IO writes for around 5 minutes? Any suggested workarounds? I already bumped up the number of Apache slots to 166% but it looks like I would have to increase the number much more to use that as a primary solution.