On Tue, Nov 29, 2005 at 01:43:17PM -0500, Steffen Plotner wrote: > I would like to add that creating backups of LVM snapshots is sensible, > as the data is in a crash-consistent state. Today's operating systems > can definitely handle this type of state. I have developed scripts that > effectively netcat contents from LVM snapshots to a remote machine > (either into another logical volume or simply a file). One other thing to point out. Any backup utility that is based on timestamps, as opposed to a file database, is going to occasionally miss changes made between the creation of the snapshot and the invocation of the backup. For example. I perform the following. - Make snapshot of /foo. - Create file /foo/bar. - Backup the /foo snapshot. At this point, the backup of /foo won't contain the file 'bar', since it was created after the snapshot was made. However, if the backup software uses the time that the backup was created, rather than the time the snapshot was created, it will think that /foo/bar would have been included in the backup, and won't catch it for future incrementals. If the backup software knows about LVM (creating the snapshots itself, for example), then it _should_ know to use the correct timestamp. My personal experience is that it is very rare to find backup software that will restore to the same filesystem at the time of backup. Even the very expensive ones don't always do the right thing. As an example, GNU tar can be coerced into doing the right thing with LVM snapshots. Something like this. # touch /tmp/snapstamp # lvcreate -s ... # mount ... # tar ... -g $lfile ... Then fix up the timestamp on the backup. # stat -c %Y /tmp/snapstamp > $lfile.bak # tail -n +2 $lfile >> $lfile.bak # mv $lfile.bak $lfile Star accepts a 'dumpdate=/tmp/snapstamp' option to use instead of current time. Dave _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
