ZRS
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VM snapshots

ZRS snapshots capture a VM's disks without its memory. Reverting restores the disks to the snapshot and discards later changes.

Take a snapshot #

  1. Open the VM and find Snapshots.
  2. Select Take snapshot.
  3. Enter a Name, such as before-upgrade, and an optional Description. An empty name uses the current time.
  4. Select Take snapshot and wait for the job to finish.

The snapshot appears in the list after creation.

Snapshots of a running VM #

A VM can be running or stopped when taking a snapshot. For a running VM with a connected guest agent, ZRS tries to freeze the guest filesystems before capturing the disks.

Memory is not captured, including application data that has not been written to disk. A filesystem-freeze warning means the snapshot was created, but the filesystems may not have been frozen.

Revert to a snapshot #

  1. Stop the VM and wait for Shutdown.
  2. In Snapshots, select the snapshot’s Revert action.
  3. Check the snapshot name and confirm with Revert.
  4. Wait for the job to finish. Start the VM when ready.

Reverting discards disk changes made after the snapshot. UEFI settings and TPM state are not reverted.

Snapshots created by ZRS leave the VM powered off after reverting. Supported snapshots marked memory restore their captured memory state and resume the VM instead.

Delete a snapshot #

Select the snapshot’s Delete action and confirm. Deleting removes the restore point without reverting the VM’s current disks.

If a snapshot is marked delete unfinished, retry deletion to finish the disk merge. That snapshot cannot be reverted to while deletion is unfinished.

Snapshot requirements #

Snapshots require libvirt 11.1.0 or newer. Every disk except CD-ROMs and floppies must be a writable qcow2 or raw image file. Shared, transient, and encrypted disks are unsupported.

ZRS cannot create new snapshots while internal snapshots exist, and cannot revert to or delete internal snapshots. Manage those snapshots outside ZRS.

Snapshot files depend on the VM’s disk images. They do not provide a separate backup if that storage fails.

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