From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stan Hoeppner Subject: Re: XFS on top RAID10 with odd drives count and 2 near copies Date: Tue, 14 Feb 2012 05:10:27 -0600 Message-ID: <4F3A4123.1050508@hardwarefreak.com> References: <4F35E925.6000003@hardwarefreak.com> <4F38FD5D.1010201@hardwarefreak.com> <20120213230228.GA5822@www5.open-std.org> <4F3A23F1.6090908@westcontrol.com> Reply-To: stan@hardwarefreak.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4F3A23F1.6090908@westcontrol.com> Sender: linux-raid-owner@vger.kernel.org To: David Brown Cc: CoolCold , keld@keldix.com, Linux RAID List-Id: linux-raid.ids On 2/14/2012 3:05 AM, David Brown wrote: > I believe that if you have XFS on LVM, then making a snapshot will first > "freeze" the filesystem, take the snapshot, then "thaw" the filesystem. > This process will sync the system, flushing out outstanding writes, and > delay new writes until the "thaw" - thus you get a bit better than a > "power-off copy". In particular, you don't get zeroed-out files no > matter what you've done with your barrier settings. xfs_freeze[1] was a feature/command carried over from IRIX to Linux during the XFS port. This functionality was later moved from the XFS layer into the VFS layer. Now FS freezing is fully automatic when an LVM snapshot is taken. Now in the VFS layer, this works with any filesystem type, EXT2/3/4, Reiser, JFS, XFS. I don't have the date or kernel rev handy where this was integrated in mainline. It's been at least a couple/few years. I'm not inclined to dig it up. [1] xfs_freeze(8) NAME xfs_freeze - suspend access to an XFS filesystem SYNOPSIS xfs_freeze -f | -u mount-point DESCRIPTION xfs_freeze suspends and resumes access to an XFS filesystem (see xfs(5)). [...] -- Stan