regex: "^manual_.*"

.. DANGER::

You might have **existing snapshots** of filesystems affected by pruning which you want to keep, i.e. not be destroyed by zrepl.

Make sure to actually add the necessary ``regex`` keep rules on both sides, like with ``manual`` in the example above.

The reason is that, by definition, all snapshots on the receiver have already been replicated to there from the sender.

To determine whether a sender-side snapshot has already been replicated, zrepl uses the :ref:`replication cursor bookmark <replication-cursor-and-last-received-hold>` which corresponds to the most recent successfully replicated snapshot.

.. ATTENTION::

If you use ``not_replicated`` in your pruning rules, make sure to :ref:`monitor <monitoring>` replication.

If your replication gets stuck then ``not_replicated`` causes snapshots to pile uip on the sender.

ZFS and especially the ``zfs`` management command are known to degrade in performance with a lot of snapshots.

Such degradation impacts zrepl, any other scripts, and human ability to manage your zpool.

.. _prune-keep-retention-grid:

Policy ``grid``