From: Alasdair G Kergon Subject: Re: [PATCH 0/3] freeze feature ver 1.8 Date: Mon, 30 Jun 2008 14:54:33 +0100 Message-ID: <20080630135433.GA22522@agk.fab.redhat.com> References: <20080630212005t-sato@mail.jp.nec.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "axboe@kernel.dk" , "mtk.manpages@googlemail.com" , "linux-kernel@vger.kernel.org" , "xfs@oss.sgi.com" , "dm-devel@redhat.com" , "viro@ZenIV.linux.org.uk" , "linux-fsdevel@vger.kernel.org" , "akpm@linux-foundation.org" , "linux-ext4@vger.kernel.org" To: Takashi Sato Return-path: Content-Disposition: inline In-Reply-To: <20080630212005t-sato@mail.jp.nec.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com List-Id: linux-ext4.vger.kernel.org On Mon, Jun 30, 2008 at 09:20:05PM +0900, Takashi Sato wrote: > Currently, ext3 in mainline Linux doesn't have the freeze feature which > suspends write requests. So, we cannot take a backup which keeps > the filesystem's consistency with the storage device's features > (snapshot and replication) while it is mounted. > In many case, a commercial filesystem (e.g. VxFS) has > the freeze feature and it would be used to get the consistent backup. > If Linux's standard filesytem ext3 has the freeze feature, we can do it > without a commercial filesystem. Is the following a fair summary? 1. Some filesystems have a freeze/thaw feature. XFS exports this to userspace directly through a couple of ioctls, but other filesystems don't. For filesystems on device-mapper block devices it is exported to userspace through the DM_DEV_SUSPEND ioctl which LVM uses. 2. There is a desire to access this feature from userspace on non-XFS filesystems without having to use device-mapper/LVM. Alasdair -- agk@redhat.com