On Thursday, February 8, 2024 6:44:50 PM CET Wols Lists wrote: > On 08/02/2024 06:38, J. Roeleveld wrote: > > ZFS doesn't have this "max amount of changes", but will happily fill up > > the > > entire pool keeping all versions available. > > But it was easier to add zpool monitoring for this on ZFS then it was to > > add snapshot monitoring to LVM. > > > > I wonder, how do you deal with snapshots getting "full" on your system? > > As far as I'm, concerned, snapshots are read-only once they're created. > But there is a "grow the snapshot as required" option. > > I don't understand it exactly, but what I think happens is when I create > the snapshot it allocates, let's say, 1GB. As I write to the master > copy, it fills up that 1GB with CoW blocks, and the original blocks are > handed over to the backup snapshot. And when that backup snapshot is > full of blocks that have been "overwritten" (or in reality replaced), > lvm just adds another 1GB or whatever I told it to.
That works with a single snapshot. But, when I last used LVM like this, I would have multiple snapshots. When I change something on the LV, the original data would be copied to the snapshot. If I would have 2 snapshots for that LV, both would grow at the same time. Or is that changed in recent versions? > So when I delete a snapshot, it just goes through those few blocks, > decrements their use count (if they've been used in multiple snapshots), > and if the use count goes to zero they're handed back to the "empty" pool. I know this is how ZFS snapshots work. But am not convinced LVM snapshots work the same way. > All I have to do is make sure that the sum of my snapshots does not fill > the lv (logical volume). Which in my case is a raid-5. I assume you mean PV (Physical Volume)? I actually ditched the whole idea of raid-5 when drives got bigger than 1TB. I currently use Raid-6 (or specifically RaidZ2, which is the ZFS "equivalent") -- Joost
