Ignore unmodified datasets

[Thalhammer]

Hi, I have a lot of datasets, which often remain unmodified for extended periods of time, but should be fairly frequently snapshoted when used (currently in 15 minute intervals). This causes tons of empty (0B used) snapshots which make viewing the list harder and might even slow zfs down a bit.

Would it be possible to ignore doing a snapshot if theres not been any write activity to the filesystem since the last snapshot ?

[MynaITLabs]

Or at least an option in 'findoid' and 'zfs list -t snapshot' to ignore/not-display snapshots which have 0 byte "USED" differences. something like "--ignore-zero-used" ?

Note: Before feature is implemented. Could also write an 'awk' script to not display lines with 2nd column "USED" being exactly " 0K ".

[jimsalterjrs]

Would it be possible to ignore doing a snapshot if theres not been any write activity to the filesystem since the last snapshot ?

No, because it would make the accounting on keeping the correct number of dailies, monthlies, etc obnoxious... And even more importantly, would mean that if you wanted to roll back to last Friday's daily, there might not BE a daily from last Friday, if nothing changed between the most recent hourly (or frequently!) and 23:59 on last Friday when the daily should have been taken.

This is a WONTFIX for the project, but you can easily create your own "cleanup" script that destroys any snapshot with 0 bytes in the USED column of zfs list -t snap.

[glibg10b]

This script returns 1 if the dataset hasn't changed since the last snapshot. It needs the libzfs module which is maintained by TrueNAS and can be installed with sudo apt install python3-libzfs on Ubuntu.

#!/bin/python3

import libzfs
import os

def exit_success_if_changed(dataset_name):
    dataset = libzfs.ZFS().get_dataset(dataset_name)
    written = dataset.properties['written'].value

    if written != '0':
        exit(0)

for dataset in os.environ['SANOID_TARGETS'].split(','):
    exit_success_if_changed(dataset)

exit(1)

To use it, add the following to /etc/sanoid/sanoid.conf:

pre_snapshot_script = /path/to/script.py
no_inconsistent_snapshot = true