Manual storage snapshotting

Certain use cases such as block storage on LVM or disks backed via storage exported through the vhost-user-blk protocol may require that snapshots are done in conjunction with the storage provider which is not managed by libvirt.

To achieve this such disks can use snapshot mode manual. When a snapshot has a disk in manual mode the following happens:

  1. libvirt takes snapshot of the VM memory if requested

  1. If a live snapshot is requested (VIR_DOMAIN_SNAPSHOT_CREATE_LIVE) the VM runs until the memory snapshot phase completes and is then paused.

  2. Otherwise the VM is paused right away.

  1. Snapshot of disks which are marked for external snapsot is executed

  2. The API return success, the VM is paused.

  3. The user snapshots the externally managed storage

  4. The user resumes the execution of the VM (virsh resume $VM)

Overview of manual snapshots

Manual snapshot of a disk is requested by setting the snapshot property to manual in the snapshot XML

  <memory file='/path/to/memory/img'/>
    <disk name='vda' snapshot='manual'/>
    <disk name='vdb' snapshot='external'/>
    <disk name='vdc' snapshot='no'/>

or --diskspec vda,snapshot=manual when using virsh snapshot-create-as:

$ virsh snapshot-create-as  --diskspec vda,snapshot=manual \
                            --diskspec vdb,snapshot=external \
                            --diskspec vdc,snapshot=no $VM \
                            --memspec file=/path/to/memory/img