From owner-freebsd-hackers@FreeBSD.ORG Tue Nov 23 19:49:51 2010 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id F18161065672 for ; Tue, 23 Nov 2010 19:49:51 +0000 (UTC) (envelope-from lidl@hydra.pix.net) Received: from hydra.pix.net (hydra.pix.net [IPv6:2001:470:e254::3c]) by mx1.freebsd.org (Postfix) with ESMTP id B019C8FC18 for ; Tue, 23 Nov 2010 19:49:51 +0000 (UTC) Received: from hydra.pix.net (localhost [127.0.0.1]) by hydra.pix.net (8.14.4/8.14.4) with ESMTP id oANJno4F074963; Tue, 23 Nov 2010 14:49:50 -0500 (EST) (envelope-from lidl@hydra.pix.net) X-Virus-Status: Clean X-Virus-Scanned: clamav-milter 0.96.3 at mail.pix.net Received: (from lidl@localhost) by hydra.pix.net (8.14.4/8.14.4/Submit) id oANJnoLW074962; Tue, 23 Nov 2010 14:49:50 -0500 (EST) (envelope-from lidl) Date: Tue, 23 Nov 2010 14:49:50 -0500 From: Kurt Lidl To: Chris St Denis Message-ID: <20101123194950.GB74848@pix.net> References: <4CEC0A27.8080900@smartt.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4CEC0A27.8080900@smartt.com> User-Agent: Mutt/1.5.21 (2010-09-15) Cc: freebsd-hackers@freebsd.org Subject: Re: UFS Snapshots and iowait X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 23 Nov 2010 19:49:52 -0000 On Tue, Nov 23, 2010 at 10:38:31AM -0800, Chris St Denis wrote: > 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? It blocks updates to the filesystem while during part of the snapshot process. See the comments in /usr/src/sys/ufs/ffs/ffs_snapshot.c I found using UFS snapshots on a production fileserver untenable during normal working hours. I have a backup fileserver that I rsync the files to, and then use the UFS snapshots there. > 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. Use ZFS. The way snapshots work there, they are nearly instantanous to create, and you are not limited to 20 snapshots per filesystem. -Kurt