+++ Thursday 10 April 2025 +++


Snapshot and rollback of virtual machines
=========================================

FreeBSD combines the power of bhyve, the hypervisor/virtual
machine manager, with the power of ZFS.

bhyve and vm-bhyve
------------------
Bhyve, the FreeBSD hypervisor/virtual machine manager is a
very efficient hypervisor.

vm-bhyve is a management system for FreeBSD bhyve virtual
machines. It simplifies the creation, use and management of
bhyve virtual machines.

ZFS snapshot and rollback
-------------------------
ZFS provides the wonderful technology to take snapshots of
ZFS datasets. A snapshots is a read-only copy of the
dataset. Initially, a snapshot doesn't consume additional
disk space. Only new changes, the difference between the
actual dataset and the snapshot, are stored.

The creation of a snapshot is practically instantaneous.

Snapshots can be cloned, and can be transferred to other
locations, either locally or remote. Cloning and
transferring are wonderful and very useful options.

Another very useful option is the rollback of a snapshot. A
rollback discards all changes in the dataset since the
creation of the snapshot and reverts it to the state at the
time the snapshot was taken.

VM snapshot
-----------
vm-bhyve is designed work with ZFS. It creates ZFS
datasets, and supports the use of snapshots and rollbacks.

First, create a new virtual machine, install and configure
the operating system on it, and perhaps additional
packages. Shut the virtual machine down and create a
snapshot of it.

The snapshot can be used in several ways. Cloning the
snapshot creates practically instantaneous a similar virtual
machine, and the snapshot can be send to a different
location either as a backup or as a method to create a
simular virtual machine locally, or on a remote host.

VM rollback
-----------
First, create a new virtual machine, install and configure
the operating system, and perhaps additional packages. Shut
the virtual machine down and create a snapshot of it.

Start using the virtual machine, f.e. for testing purposes.
Install packages, make use of the software, and so on.

When done, shut the machine down and issue a rollback.
Again, performing a rollback is instantaneous. The virtual
machine is rolled back to its pristine state at the time
the snapshot was taken.

Start the virtual machine, use it, shut it down, and
rollback again. This process can be repeated as often as
needed.

New snapshots
-------------
As the virtual machine ages, maintenance becomes important.
an upgrade might be needed. or a change in the
configuration.

Start the virtual machine, perform the maintenance, shut it
down and create a new snapshot. This new snapshot can be
used just like the previous, either to rapid deployment of
similar virtual machines or for temporarily use (e.g., for
testing) followed by a rollback.

Happy vm-ing!


Last edited: $Date: 2025/04/10 15:56:12 $