How to have ZFS make snapshots of a directory only when files are changed

filesystemssnapshotzfs

Is it possible to have ZFS make snapshots of a filesystem i.e. pool/filesystem/ only when files are changed? Instead of using cron or something to automatically create a snapshot every 5 minutes is it possible to have ZFS automatically take snapshots after a file has changed?

Is this possible and what would it involve? How would you do it?

Thanks in advance.

Best Answer

Multiple Options:

1) cron based zfs diff (Solaris 11 Express++) and if something changed -> Snapshot() 2) dtrace zfs snapshot trigger

I have not done the latter, but read about it. 1) is probably the easiest way to do something, altought you might miss some changes, but you will not have snapshots with no changes piling up.

Regards, Robert

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Large number of snapshots on a ZFS system

There's no problem with lots of snapshots. Having thousands of ZFS filesystems can cause boot times of more than an hour, but you're not doing that.

How to Delete All but Last N ZFS Snapshots

You may find something like this a little simpler

zfs list -t snapshot -o name | grep ^tank@Auto | tac | tail -n +16 | xargs -n 1 zfs destroy -r

Output the list of the snapshot (names only) with zfs list -t snapshot -o name
Filter to keep only the ones that match tank@Auto with grep ^tank@Auto
Reverse the list (previously sorted from oldest to newest) with tac
Limit output to the 16th oldest result and following with tail -n +16
Then destroy with xargs -n 1 zfs destroy -vr

Deleting snapshots in reverse order is supposedly more efficient or sort in reverse order of creation.

zfs list -t snapshot -o name -S creation | grep ^tank@Auto | tail -n +16 | xargs -n 1 zfs destroy -vr

Test it with ...|xargs -n 1 echo.

Best Answer

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Large number of snapshots on a ZFS system

How to Delete All but Last N ZFS Snapshots

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