红帽全球峰会第 14 章 Saving and restoring virtual machine state by using snapshots
To save the current state of a virtual machine (VM), you can create a snapshot of the VM. Afterwards, you can revert to the snapshot to return the VM to the saved state.
A VM snapshot contains the disk image of the VM. If you create a snapshot from a running VM, also known as a live snapshot, the snapshot also contains the memory state of the VM, which includes running processes and applications.
Creating snapshots can be useful, for example, for the following tasks:
- Saving a clean state of the guest operating system
- Ensuring that you have a restore point before performing a potentially destructive operation on the VM
To create a VM snapshot or revert to one, you can use the command line (CLI) or the RHEL web console.
14.1. Support limitations for virtual machine snapshots
Red Hat supports the snapshot functionality for virtual machines (VMs) on RHEL only when you use external snapshots. Currently, you can create external snapshots on RHEL only when all of the following requirements are met:
- The VM is using file-based storage.
You create the VM snapshot only in one of the following scenarios:
- The VM is shut-down.
-
If the VM is running, you use the
--disk-only --quiesceoptions or the--live --memspecoptions.
Most other configurations create internal snapshots, which are deprecated in RHEL 10. Internal snapshots might work for your use case, but Red Hat does not provide full testing and support for them.
Do not use internal snapshots in production environments.
To ensure that a snapshot is supported, display the XML configuration of the snapshot and check the snapshot type and storage:
# virsh snapshot-dumpxml <vm-name> <snapshot-name>Example output of a supported snapshot:
<domainsnapshot> <name>sample-snapshot-name-1<name> <state>shutoff</state> <creationTime>1706658764</creationTime> <memory snapshot='no'/> <disks> <disk name='vda' snapshot='external' type='file'> <driver type='qcow2'/> <source file='/var/lib/libvirt/images/vm-name.sample-snapshot-name-1'/> </disk> </disks> <domain type='kvm'> [...]Example output of an unsupported snapshot:
<domainsnapshot> <name>sample-snapshot-name-2</name> <state>running</state> <creationTime>1653396424</creationTime> <memory snapshot='internal'/> <disks> <disk name='vda' snapshot='internal'/> <disk name='sda' snapshot='no'/> </disks> <domain type='kvm'> [...]
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