Znapper - Znap your Snaps

Znapper is a tool to help automate zfs snapshot management on larger pools. This is similar to zfs-auto-snap, but goes a bit further to help manage snapshots over replicated pools for backups within a single host.

Auto snapshot management

To automatically snapshot all pools on your system which have mounted filesystems:

znapper snapshot

To clean-up old automatic snapshots

znapper snapshot_cleanup 
    
    
     
znapper snapshot_cleanup tank 48

    
   

Replication management

This is really what znapper was designed to do. Let's say you have two pools, a smaller nvme pool and a larger disk backed pool named tank.

On the smaller nvme pool, because it's smaller we can not keep as many snapshots due to space limitations. We want to replicate nvme to tank for archival / redundancy, but also to allow extended snapshots to be stored in tank.

To initialise the replication:

znapper init_repl 
    
    
     
znapper init_repl nvme tank/nvme

    
   

To then do an incremental replication

znapper repl 
    
    
     
znapper repl nvme tank/nvme

    
   

How does it work?

The reason auto snapshot only snapshots mounted filesystems is so that any replication target (ie tank/nvme) is NOT snapshot hourly in the background.

This is also why snapshot cleanup requires a pool name, because when snapshots are sent from nvme to tank, we can then cleanup tank/nvme's auto snapshots based on tank's policy which can be longer than the nvme policy.

Replication uses different snapshots as points in times for replication, so even removing all the auto snapshots on either side will NOT break the replication process.

Any replicated filesystem is not mounted and marked as read-only in the process. To restore from one of these snapshots, you can either zfs send back to the original pool, or temporarily mount the fs to manually recover.

Example systemd service files to automate this process.

# zfs-auto-snapshot-hourly.service
[Unit]
Description=ZFS hourly snapshot service

[Service]
Type=oneshot
ExecStart=znapper snapshot
ExecStart=znapper snapshot_cleanup tank 72
ExecStart=znapper snapshot_cleanup nvme 24

zfs-auto-snapshot-hourly.timer
[Unit]
Description=ZFS hourly snapshot timer

[Timer]
OnCalendar=hourly
Persistent=true

[Install]
WantedBy=timers.target

zfs-auto-replicate-daily.service
[Unit]
Description=ZFS daily replicate service

[Service]
Type=oneshot
ExecStart=znapper repl nvme tank/nvme

zfs-auto-replicate-daily.timer
[Unit]
Description=ZFS daily replicate timer

[Timer]
OnCalendar=*-*-* 18:00:00
Persistent=true

[Install]
WantedBy=timers.target