How to delete all but last [n] ZFS snapshots?

Question

I'm currently snapshotting my ZFS-based NAS nightly and weekly, a process that has saved my ass a few times. However, while the creation of the snapshot is automatic (from cron), the deletion of old snapshots is still a manual task. Obviously there's a risk that if I get hit by a bus, or the manual task isn't carried out, the NAS will run out of disk space.

Does anyone have any good ways / scripts they use to manage the number of snapshots stored on their ZFS systems? Ideally, I'd like a script that iterates through all the snapshots for a given ZFS filesystem and deletes all but the last n snapshots for that filesystem.

E.g. I've got two filesystems, one called tank and another called sastank. Snapshots are named with the date on which they were created: sastank@AutoD-2011-12-13 so a simple sort command should list them in order. I'm looking to keep the last 2 week's worth of daily snapshots on tank, but only the last two days worth of snapshots on sastank.

score 56 · Accepted Answer · edited Jan 09 '20 at 20:29

56

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.

edited Jan 09 '20 at 20:29

M. Rostami

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answered Dec 14 '11 at 12:59

user9517

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I think this needs a `sort -r` before the `sed` command. `sed` seems to output the bottom of the list beyond the first 15 lines, which in the default sort is the most recent. Flipping the list means I get the oldest snapshots at the bottom. – growse Dec 14 '11 at 14:14
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He stated "deleting snapshots in reverse order is supposedly more efficient", thus the sort order. – tgunr Mar 17 '17 at 18:03

score 33 · Answer 2 · answered Nov 11 '16 at 02:21

This totally doesn't answer the question itself, but don't forget you can delete ranges of snapshots.

zfs destroy zpool1/dataset@20160918%20161107

Would destroy all snapshots from "20160918" to "20161107" inclusive. Either end may be left blank, to mean "oldest" or "newest". So you could cook something up that figures out the "n" then destroy "...%n"..

Sorry to resurrect an old question.

score 25 · Answer 3 · answered Sep 01 '13 at 10:20

More general case of getting most recent snapshot based on creation date, not by name.

zfs list -H -t snapshot -o name -S creation | head -1

Scoped to a specific filesystem name TestOne

zfs list -H -t snapshot -o name -S creation -d1 TestOne | head -1

-H:No header so that first line is a snapshot name

-t snapshot: List snapshots (list can list other things like pools and volumes)

-o name: Display the snapshot name property.

-S creation: Capital S denotes descending sort, based on creation time. This puts most recent snapshot as the first line.

-d1 TestOne: Says include children, which seems confusing but its because as far as this command is concerned, snapshots of TestOne are children. This will NOT list snapshots of volumes within TestOne such as TestOne/SubVol@someSnapshot.

| head -1: Pipe to head and only return first line.

Thanks for the `-d1`. That was the key to the question "How do I get all snapshots for a given dataset?" — Jonathon Reinhart, Dec 28 '16 at 19:12

Dan Buhler · Answer 4 · 2012-08-17T20:02:08.643

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growse's didn't work on OpenIndiana for me. It didn't understand -0 for xargs.

If using sort, be aware that it sorts alphabetically which may not be desired as you are probably wanting to find the most recent.

Here is code that will delete all but the last snapshots.

Remove the 'echo' to go live.

RETENTION=5
FS=tank1/test
SNAPNAME=daily-

zfs list -t snapshot -o name | grep ^$FS@${SNAPNAME} |  sed -n -e :a -e '1,${RETENTION}!{P;N;D;};N;ba' | xargs -n 1 echo zfs destroy -r

Sources: http://sed.sourceforge.net/sed1line.txt

edited Aug 17 '12 at 20:02

answered May 25 '12 at 23:01

Dan Buhler

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Upvote because anyone who can use sed like that deserves it. – growse May 25 '12 at 23:05
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After a recent software update, that sed string stopped working for me and it started deleting all snapshots! bad sed! Luckily the production server was old and stayed safe. I now use sed -n -e :a -e '1,${RETENTION}!{P;N;D;};N;ba' – Dan Buhler Aug 17 '12 at 19:58
I've never seen anyone SED like that. – Jason Aug 08 '17 at 02:44

score 6 · Answer 5 · answered Jan 09 '20 at 20:18

6

You might also want to check out zfs-prune-snapshots.

Remove snapshots from one or more zpools that match given criteria

It has a fairly robust time based mechanism for deleting snapshots, an example from the docs:

Remove snapshots older than two months on the tank pool that end with the string "_frequent"

zfs-prune-snapshots -s '_frequent' 2M tank

answered Jan 09 '20 at 20:18

DRAD

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wow! nice&&neat. doing exactly what is needed – ataraxic Jan 02 '21 at 13:18
This should be updated to be the accepted answer, much cleaner than all the bash-fu. – Kurtosis Jul 29 '21 at 15:10

score 3 · Answer 6 · answered Dec 14 '11 at 12:58

I may have solved this with some bash-fu.

 zfs list -t snapshot -o name | grep ^tank@AutoD- | sort -r | wc -l | xargs -n 1 expr -$NUM_TO_KEEP + | tr -d '\n' | xargs -0 -i bash -c "zfs list -t snapshot -o name | grep ^tank@AutoD- | sort -r | tail -n{} | sort |xargs -t -n 1 zfs destroy -r"

Wow. It feels so wrong.

score 2 · Answer 7 · answered Jul 29 '20 at 21:02

Just wanted to chime in on how I'm doing this on FreeBSD and OmniOS:

Get number of snapshots:

zfs list -t snapshot -o name | grep ^tank@Auto | wc -l
141

Subtract number you want to leave for n (e.g. 30 for a month of latest daily snapshots):

zfs list -t snapshot -o name | grep ^tank@Auto |  head -n +111 | xargs -n 1 zfs destroy -vr

Note how I replaced tail with head to delete in order from oldest to newest, since there's no tac command on FreeBSD

That's it! Works great for me...

score 1 · Answer 8 · answered Jul 06 '21 at 23:17

Identify the latest two snapshots for a given dataset (creation, newest to oldest)

zfs_latest=`zfs list -H -t snapshot -o name -S creation | grep ^tank/example_dataset@ | head -2`

Identify ALL snapshots for a given dataset (creation, newest to oldest)

zfs_delete=`zfs list -H -t snapshot -o name -S creation | grep ^tanks/example_dataset@`

Remove latest snapshots from all set; creating a list of snapshots to delete.

for keep_snap in ${zfs_latest[@]}; do
  zfs_delete=( "${zfs_delete[@]/$keep_snap}" );
done

Remove the old snapshots

for snap in ${zfs_delete[@]}; do
  zfs destroy ${snap}
done

score 1 · Answer 9 · edited Oct 17 '12 at 12:41

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The path for head is needed on Solaris, but should work without the path on other distros.

retention=14
dataset=vmstorage-17/824

zfs list -rt snap -H -o name ${dataset} | \
/usr/gnu/bin/head -n -${retention} | xargs -n 1 zfs destroy -r

edited Oct 17 '12 at 12:41

Thomas Berger

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answered Oct 16 '12 at 16:41

Josh Simon

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How to delete all but last [n] ZFS snapshots?

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