phantom snapshots

[Paul Kraus]

> On Sep 2, 2016, at 3:41 PM, Linda Kateley <lkateley at kateley.com> wrote:
> 
> How did you remove the files in the snapshot? I keep trying but it is read-only? Can I remount it read-write?

Snapshots are by design read only copies of the data.

When you create a ZFS snapshot you are (functionally) copying the Uberblock for the dataset and preventing any slabs used by it from being added to the free list. This is partly why ZFS snapshots have little to no performance penalty.

When you clone a snapshot you are effectively making a read-write copy of it.

So to delete files from a snapshot you destroy the snapshot itself. If the snapshot has already been destroyed, then you _may_ be running into the delayed snapshot destruction implemented a bunch of years ago for some really good reasons. If a system rebooted in the midst of a snapshot destruction, the reboot would not complete until the snapshot destruction was completely done. For large snapshots this could be hours (or even days).

So the zfs destroy <snapshot> command returns once the snapshot has been scheduled to be destroyed, not after the snapshot has been completely destroyed. How big are these datasets and snapshots ?