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Volume backup and revert
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With Qubes, it is possible to revert one of a VM’s storage volumes to a
previous state using the automatic snapshot that is normally saved every
time a VM is shutdown. (Note that this is a different, lower level
activity than the :doc:`Backup, Restoration, and Migration </user/how-to-guides/how-to-back-up-restore-and-migrate>` process.)

In Qubes, when you create a new VM, it’s volumes are stored in one of
the system’s :doc:`Storage Pools </user/advanced-topics/secondary-storage>`. On pool creation,
a revisions_to_keep default value is set for the entire pool. (For a
pool creation example, see :doc:`Storing app qubes on Secondary Drives </user/advanced-topics/secondary-storage>`.) Thereafter, each volume associated
with a VM that is stored in this pool inherits the pool default
revisions_to_keep.

For the private volume associated with a VM named vmname, you may
inspect the value of revisions_to_keep from the dom0 CLI as follows:

.. code:: bash

      qvm-volume info vmname:private



The output of the above command will also display the “Available
revisions (for revert)” at the bottom. For a very large volume in a
small pool, revisions_to_keep should probably be set to the minimum
value of 1 to minimize the possibility of the pool being accidentally
filled up by snapshots. For a smaller volume for which you would like to
have the future option of reverting, revisions_to_keep should probably
be set to at least 2. To set revisions_to_keep for this same VM / volume
example:

.. code:: bash

      qvm-volume config vmname:private revisions_to_keep 2



With the VM stopped, you may revert to an older snapshot of the private
volume from the above list of “Available revisions (for revert)”, where
the last item on the list with the largest integer is the most recent
snapshot:

.. code:: bash

      qvm-volume revert vmname:private <revision>