ZFS / BTRFS Auto Snapshot

This script emulates NetApp Snapshots Schedules on ZFS and BTRFS. Somewhat related to Apple Time Machine.

How does it work exactly?

Snapshot are automatically created on a schedule. Aging and eventually deleting oldest snapshots. As an example lets consider a "hourly" schedule with maximum 4 snapshots:

zfs destroy myvol@hourly3
zfs rename myvol@hourly2 myvol@hourly3
zfs rename myvol@hourly1 myvol@hourly2
zfs rename myvol@hourly0 myvol@hourly1
zfs snapshot myvol@hourly0

The oldest snapshot 3 is deleted, other snapshots are progressively aged / renamed from 0 -> 1, 1 -> 2, 2 -> 3 etc. Finally a new snapshot 0 is created.

Why?

Most commonly to protect from accidental file removal or changes, undelete, or restore an older version. Snapshots are NOT backups, but if you delete something it's faster to copy it from a snapshot than recover from a backup.

🛑 WARNING USE AT YOUR OWN RISK 🛑

I take no responsibility for any data loss associated with use of these scripts! If used incorrectly the script may delete your volumes and data. Snapshots are not backups. Make sure to back up your data before use.

Usage

Place either ZFS or BTRFS autosnap.sh in a directory accessible via PATH for Cron. The script is recursive so it will need to call itself by "${0}".
If using BTRFS edit the script and specify mount point and snapshots directory.
Add crontab(5) entries for root. You can come up with any schedule you want. See examples below.

Note, when running for the very first time, or first round of snapshots you will get errors because there is no oldest snapshot to delete or older snapshots to rename. Thats normal, just ignore.

Example crontab(5) with 4 types

0 * * * * autosnap.sh myvol hourly  3  # four hourly snapshots
0 0 * * * autosnap.sh myvol daily   6  # a week worth of daily snapshots
0 0 * * 0 autosnap.sh myvol weekly  3  # month worth if weekly snapshots
0 0 1 * * autosnap.sh myvol monthly 11 # a year worth of monthly snapshots

Note that system /etc/crontab has a different format than user crontab(5). Crontab format may also differ between operating systems and cron versions.

Syntax Explanation

The syntax is: zrs.sh <volname> <type> <#max>
Volname is a ZFS/BTRFS volume name.
Type is the name of a schedule for example hourly, daily, weekly, mickey_mouse, donald_duck. It can also be empty "" if you have only one schedule.
The 3rd parameter is the max snapshot number in sequence starting from 0, or number of snapshots -1.
Example: autosnap.sh mypics hourly 7 will produce 8 snapshots named hourly0 to hourly7

Legal Stuff

Copyright (c) 2021-2022 by Google LLC
This is not an official Google product
License: Apache 2.0

tenox7/autosnap