From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mikulas Patocka Subject: Re: LVM Snapshot Feature Date: Mon, 4 Aug 2008 09:15:11 -0400 (EDT) Message-ID: References: <4DE0C34D8B0DA64C9585DC45C36EA03BAB0788@dewdfe1g.wdf.sap.corp> <1746B17C-CC23-40D7-A993-FC32CAA5BF24@gmail.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Return-path: In-Reply-To: <1746B17C-CC23-40D7-A993-FC32CAA5BF24@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: device-mapper development List-Id: dm-devel.ids On Fri, 1 Aug 2008, Adam Hamsik wrote: > On Aug,Friday 1 2008, at 9:35 AM, Bombardier, Pascal wrote: > > > Hi, > > > > In your opinion, does it make sense to be able to create non-persistent > > snapshots ? > > In the case of a filesystem backup, a non-persistent snapshot would be a > > snapshot that we agree to lose in case of failure or reboot. If anything > > happens, a server administrator would have to recreate a new snapshot > > and then restart the backup. > > In this case, I think metadata could be stored in memory instead of on > > disk, which should improve LVM snapshot performance. > > > > Is this theory wrong, and is this something which can be implemented > > easily in the current LVM code ? > > > > AFAIK non-persistent snapshots are already implemented see > DM_PERSISTENT_DEV_FLAG ? I haven't look at linux kernel code how is > it done but when I solve my lvcreate -s bug on NetBSD non-persistent > snapshots are next :). > > Regards > > Adam. Yes. They are implemented in device mapper in kernel --- but no userspace lvm tool can use them. You can only create them using dmsetup. Mikulas