linux

Snapshot for KVM via libvirt with virsh

noraj (Alexandre ZANNI)
, ,
🇬🇧

Context#

I am using KVM, and use/manage my VMs with virt-manager. But I asked myself this question: how can create or revert some snapshot?

I'm giving examples for qcow2 disk images and commands are made with virsh.

Internal Disk Snapshots#

You can list available VM with virsh in order to know their name:

$ virsh list
 Id Name                 State
----------------------------------
  1 vmname               running

Then you can check if there already is existing shapshots for this VM:

$ virsh snapshot-list vmname
 Name                 Creation Time             State
------------------------------------------------------------

Next there is two possibilities to make a snapshot:

  • create a XML snapshot description file to specify the name and description of the snapshot
  • or let libvirt choose a name and no description

The XML snapshot description file must look like the following:

<domainsnapshot>
    <name>vmname-snapshot1</name>
    <description>description of the snapshot</description>
</domainsnapshot>

Make a snapshot with an XML file:

$ virsh snapshot-create vmname /path/to/description.xml

Or make a snapshot without description file:

$ virsh snapshot-create vmname

Note: this is much more faster to make a snapshot while the VM is stoped. But it's also possible to make a snapshot while the VM is running even if it's more slow.

If you want to see some information about the VM and snapshots you can run:

$ qemu-img info /path/to/disk/image/vmname.qcow2
image: vmname.qcow2
file format: qcow2
virtual size: 20G (21474836480 bytes)
disk size: 5.2G
cluster_size: 65536
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
1         vmname-snapshot1   329M 2017-02-08 20:40:59   01:23:38.281
2         vmname-snapshot2   375M 2017-02-08 20:46:39   01:26:01.645
3         vmname-snapshot3   482M 2017-02-08 22:42:48   03:22:00.515
Format specific information:
    compat: 1.1
    lazy refcounts: true
    refcount bits: 16
    corrupt: false

To revert the VM to a snapshot, for example run:

$ virsh snapshot-revert vmname vmname-snapshot1

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