Snapshot

Create a Snapshot

About to do something dangerous? Let’s create a ‘save’ point so you can reload your game, so to speak. They don’t take any space (to start with) and are nearly instant.

# Create a snapshot named `save-1`
zfs snapshot pool01/archive@save-1

The snapshot is a read-only copy of the filesystem at that time. It’s mounted by default in a hidden directory and you can examine and even copy things out of it, if you desire.

ls /srv/archive/.zfs/save-1

Delete a Snapshot

While a snapshot doesn’t take up any space to start with, it begins to as you make changes. Anything you delete stays around on the snapshot. Things you edit consume space as well for the changed bits. So when you’re done with a snapshot, it’s easy to remove.

zfs snapshot destroy pool01/archive@save-1

Rollback to a Snapshot

Mess things up in your archive folder after all? Not a problem, just roll back to the same state as your snapshot.

zfs rollback pool01/archive@save-1

Importantly, this is a one-way trip back. You can’t branch and jump around like it was a filesystem multiverse of alternate possibilities. ZFS will warn you about this and if you have more than one snapshot in between you and where you’re going, it will let you know they are about to be deleted.

Auto Snapshot

One of the most useful tools is the zfs-auto-snapshot utility. This will create periodic snapshots of your filesystem and keep them pruned for efficiency. By default, it creates a snapshot every 15 min, and then prunes them down so you have one:

• Every 15 min for an hour
• Every hour for a day
• Every day for a week
• Every week for month
• Every month

Install with the command:

sudo apt install zfs-auto-snapshot

That’s it. You’ll see new folders based on time created in the hidden .zfs folder at the root of your filesystems. Each filesystem will get it’s own. Anytime you need to look for a file you’ve deleted, you’ll find it there.

# Look at snapshots
ls /srv/archive/.zfs/

Excluding datasets from auto snapshot

# Disable
zfs set com.sun:auto-snapshot=false rpool/export

Excluding frequent or other auto-snapshot

There are sub-properties you can set under the basic auto-snapshot value

zfs set com.sun:auto-snapshot=true pool02/someDataSet
zfs set com.sun:auto-snapshot:frequent=false  pool02/someDataSet

zfs get com.sun:auto-snapshot pool02/someDataSet
zfs get com.sun:auto-snapshot:frequent pool02/someDataSet

# Possibly also the number to keep if other than the default is desired
zfs set com.sun:auto-snapshot:weekly=true,keep=52

# Take only weekly
zfs set com.sun:auto-snapshot:weekly=true rpool/export

Deleting Lots of auto-snapshot files

You can’t use globbing or similar to mass-delete snapshots, but you can string together a couple commands.

# Disable auto-snap as needed
zfs set com.sun:auto-snapshot=false pool04
zfs list -H -o name -t snapshot | grep auto | xargs -n1 zfs destroy

Missing Auto Snapshots

On some centOS-based systems, like XCP-NG, you will only see frequent snapshots. This is because only the frequent cron job uses the correct path. You must add a PATH statement to the other cron jobs

https://forum.level1techs.com/t/setting-up-zfs-auto-snapshot-on-centos-7/129574/12

Next Step

Now that you have snapshots, let’s send them somewhere for backup with replication.

References

https://www.reddit.com/r/zfs/comments/829v5a/zfs_ubuntu_1604_delete_snapshots_with_wildcard/