Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
drbd at bobich.net schrieb: > On Thu, 14 Feb 2008, Leroy van Logchem wrote: > >>> Here, it tells LVM2 can be used for creating snapshots. >> >> Caution: LVM2 snapshots become very slow if the amount of changes >> increases due copy-on-write. Add the additional seeks and you have a >> much lower write speed left. >> The last time I tried it reduced the write speed to 15% of the normal >> throughput. > > Indeed, and the more snapshots you have, the worse it gets, because the > overwritten data has to be copied to each of the snapshots, since they > are just sparse undo logs. This might get interesting one day: http://www.zumastor.org/ http://zumastor.googlecode.com/svn/trunk/doc/zumastor-howto.html#_snapshots 2.1. Snapshots Snapshots can be useful as part of an hourly backup system. Instead of shutting down all applications for the entire duration of the backup, you can shut them down for just the second or two needed to take a snapshot. If your goal is to protect users from accidental deletion of files, you may want to take snapshots every hour, and leave the last few snapshots around; users who accidentally delete a file can just look in the snapshot. LVM already lets administrators create snapshots, but its design has the surprising property that every block you change on the original volume consumes one block for each snapshot. The resulting speed and space penalty usually makes the use of more than one or two snapshots at a time impractical. Zumastor keeps all snapshots for a particular volume in a common snapshot store, and shares blocks the way one would expect. Thus making a change to one block of a file in the original volume only uses one block in the snapshot store no matter how many snapshots you have. -- Tomasz Chmielewski http://wpkg.org