zfssnap

zfssnap is a python script that automates the task of creating snapshots and/or replicating snapshots on ZFS on Linux systems.

As ZFS properties are used to identify the snapshot label the snapshot names are compatible with the shadow_copy2 module in Samba for use with Previous Versions.

It is made for the following purposes:

• Manage automatic snapshoting
• Manage dataset replication between network connected hosts
• Manage file based replication between one-way connected or disconnected hosts

Requirements

• Tested on Debian Jessie and Stretch
• ZFS on Linux packages
• pv
• Python >= 3.4
• Python modules: yaml, python-dateutil, scandir (Python < v3.5 only)

ZFS properties used

• zfssnap:label=[str]: Identifies the label of the snapshot.
• zfssnap:repl_status=[str]: Used to keep replication state of a snapshot
• zfssnap:version=[str]: zfssnap version used to create the snapshot

Configuration

zfssnap expects the configuration file to be located at /etc/zfssnap/zfssnap.yml. You can override this location using the --config argument.

In versions before v3.0.0 zfssnap stored its configuration in ZFS properties and had many more command line arguments, but this proved confusing, inflexible and unmanagable in more complex setups. ZFS properties are now only used for keeping state and information about the snapshot, while the configuration is stored in the configuration file.

A very simple config for snapshotting all datasets non-recursively could look like this:

cmds:
  zfs: /sbin/zfs

policies:
  snapshot-all:
    type: snapshot
    keep:
      hourly: 24
      daily: 7
      weekly: 5

See the example configuration file for more information.

Usage

zfssnap works with the concept of policies. These are defined in the YAML based configuration file. An example file is provided with the source. Running the command normally just involves pointing to a policy name.

Create a snapshot of all ZFS file systems defined in the policy snapshot-all.

./zfssnap.py --policy snapshot-all

Remove all snapshots for a policy or re-initialize a replication policy

./zfssnap.py --policy snapshot-all --reset

List config, datasets and snapshots belonging to a policy

./zfssnap.py --policy snapshot-all --list snapshots

List all options

./zfssnap.py --help

Schedule snapshots

To schedule snapshots crontab are normally used. This is an example root crontab for this purpose:

*/15 *      *  *  *   /usr/local/bin/zfssnap --log-level WARNING --policy snapshot-all
*/5  *      *  *  *   /usr/local/bin/zfssnap --log-level WARNING --policy replicate-vms

• zfssnap.py has been symlinked to /usr/local/bin/zfssnap for ease of use.
• --quiet can be used to supress all output, even warnings and errors. However, you are normally interested in getting a notification from cron if something goes wrong.

Samba configuration for Previous Version

The .zfs directory can remain hidden.

[global]
shadow: snapdir = .zfs/snapshot
shadow: sort = desc
shadow: format = zfssnap_%Y%m%dT%H%M%SZ
shadow: localtime = no

[<some share>]
vfs_objects = shadow_copy2

Development

Run tests

Install pytest (preferably in a virtual environment):

pip3 install pytest pytest-cov

Ensure you are standing in the project root:

PYTHONPATH=src/ pytest --cov=zfssnap