From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <38C5C23F.10C2F1AF@msede.com> Date: Wed, 08 Mar 2000 04:00:15 +0100 From: Michael Marxmeier MIME-Version: 1.0 Subject: Re: [linux-lvm] Snapshot documentation References: Content-Transfer-Encoding: 7bit Sender: owner-linux-lvm Errors-To: owner-linux-lvm List-Id: Content-Type: text/plain; charset="us-ascii" To: Jay Weber Cc: linux-lvm@msede.com Jay Weber wrote: > Been playing with snapshots and am noticing I can create a snapshot with > less PE's than my source LV that I'm snapshotting, with the small side > effect of: > > lvcreate -- WARNING: all snapshots will be disabled if more than 12 MB are > changed For now snapshots use a COW model at the block level. Each modified block gets saved (once) to the snapshot area. If the space dedicated to the snapshot area is exhausted the snapshot is discarded (and the the saved blocks are simply discarded). Otherwise the fs would become inconsistent. When/if LVM once has persistent snapshots this might need to change. > Is the above message implying that if I change more than 12MB of data on > my source LV that the snapshot is then defunct/useless? Does that include > deletes, etc? Yes. Though deletes should only affect the inode and lists of indirect blocks (if any) so deleting a 12MB files does not necessarily result in 12MB of changes. Hope this helps Michael -- Michael Marxmeier Marxmeier Software AG E-Mail: mike@msede.com Besenbruchstrasse 9 Phone : +49 202 2431440 42285 Wuppertal, Germany Fax : +49 202 2431420 http://www.msede.com/