[ZFS] Destroy snapshots

Snapshots in ZFS aren’t cumulative. They just include the difference between the filesystem at the time you took the snapshot and now.
Meaning if you have snapshots A, B and C, deleting A doesn’t impact the status of the remaining B and C. This is a common point of confusion when coming from other systems where you might have to consolidate snapshots to get to a consistent state.

This means, you can delete snapshots out of the middle of a list and not screw up snapshots before or after the one you deleted. So if you have:

pool/dataset@snap1 
pool/dataset@snap2 
pool/dataset@snap3 
pool/dataset@snap4 
pool/dataset@snap5

You can safely sudo zfs destroy pool/dataset@snap3 and 1, 2, 4, and 5 will all be perfectly fine afterward.

You can estimate the amount of space reclaimed by deleting multiple snapshots by doing a dry run (-n) on zfs destroy like this:

sudo zfs destroy -nv pool/dataset@snap4%snap8
would destroy pool/dataset@snap4
would destroy pool/dataset@snap5
would destroy pool/dataset@snap6
would destroy pool/dataset@snap7
would destroy pool/dataset@snap8
would reclaim 25.2G

List your snapshots (for a specific dataset simply use grep):

sudo zfs list -rt snapshot | grep pool/dataset

If you need to free some space, you can sort zfs snapshots by size:

zfs list -o name,used -s used -t snap

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