NAME

zfs-snapshot-mgmt —

automate creation of new and removal of stale ZFS snapshots

SYNOPSIS

zfs-snapshot-mgmt

DESCRIPTION

The utility creates ZFS snapshots and removes snapshots it has created that are stale. Rules for creating and removing are defined in the configuration file.

zfs-snapshot-mgmt is designed to be run by the cron(8) utility.

CONFIGURATION

zfs-snapshot-mgmt reads settings from the /usr/local/etc/zfs-snapshot-mgmt.conf file.

General Structure

The file is in the YAML format: it contains keys and values separated by a colon (:). Each value may span multiple lines and be a list or a map with key-value pairs. The indentation is always a multiple of two spaces.

There are two top-level options:

snapshot_prefix: prefix for snapshots created and recognised by this tool. All created snapshots will have names consisting of this prefix and current date and time. Only snapshots beginning with this prefix will be considered for removal.
filesystems: the main part of configuration - specifies rules for creating and removing snapshots at each filesystem. The value for this key contains keys for each filesystem (as seen by ZFS, e.g. tank/home) with snapshot creation and preservation settings.

There is an example configuration in the EXAMPLES section.

Creation Rules

For each filesystem there is one snapshot creation_rule defined. It specifies when snapshots for the particular filesystem should be created. It has two parameters. All values are specified in minutes.

at_multiple: defines how often should a snapshot be created. E.g. a value of 60 means that a snapshot is to be created every hour.
offset: defines an offset from midnight that is to be applied to the parameter. E.g. specifying a value of 30 means that the first snapshot will be taken 30 minutes after midnight.

Preservation Rules

These rules specify which of the created snapshots should be preserved. All that do not match the any of the rules and whose names begin with snapshot_prefix are destroyed.

Each of the rules has three parameters:

for_minutes: specifies how long after snapshot creation is the rule applicable.
at_multiple: analogous to the same parameter for creation_rule - snapshots whose creation time (in minutes since midnight) is a multiple of this value are retained.
offset: analogous to the same parameter for creation_rule - applies to at_multiple.

EXAMPLES

Crontab Configuration

To invoke the program every five minutes you may add the following line to the /etc/crontab configuration file:

*/5 * * * * root /usr/local/bin/zfs-snapshot-mgmt

Bear in mind that this effectively limits the resolution to 5 minutes.

zfs-snapshot-mgmt.conf

Here is an example configuration.

snapshot_prefix: auto-
filesystems:
  tank/usr/home:
    creation_rule:
      at_multiple: 5
      offset: 0
    preservation_rules:
      - { for_minutes:    90, at_multiple:    0, offset:    0 }
      - { for_minutes:   720, at_multiple:   30, offset:    0 }
      - { for_minutes: 10080, at_multiple:  180, offset:  120 }
  tank/usr:
    recursive: true
    creation_rule:
      at_multiple: 1440
      offset: 1200
    preservation_rules:
      - { for_minutes: 5760, at_multiple: 1440, offset: 1200 }

which specifies the following settings:

names of created snapshots start with auto- and only such snapshots are considered for removal.
there are two filesystems: tank/usr/home and tank/usr.
snapshots for tank/usr/home are created every five minutes, starting at midnight.
all snapshots for tank/usr/home are kept for 90 minutes after creation.
only snapshots created af full and half hour are retained for 12 hours (720 minutes) after creation for tank/usr/home.
snapshots created at multiple of three hours starting with 2 a.m. are retained for a week (10080 minutes) after creation for tank/usr/home. This means: 2 a.m., 5 a.m., 8 a.m. and so on.
snapshots on tank/usr are created once a day at 20 p.m. and retained for 4 days.
snapshots are taken recursively on tank/usr filesystem and all filesystems mounted under it.

FILES

/usr/local/etc/zfs-snapshot-mgmt.conf The configuration file

AUTHORS

Marcin Simonides ⟨marcin@studio4plus.com⟩

BUGS

There is no way to use alternative path for the configuration file.