Single Disk Snapshot

Summary

Customization of snapshots with regards to VM configuration and disks.

Owner

• Name: Daniel Erez (Derez)
• Email: derez@redhat.com

Current status

• Target Release: 3.4
• Status: released

Benefit to oVirt

• Allow creation of a customized snapshot. I.e. selecting which disks to take snapshot on.
• Custom snapshot preview:
  • Previewing a new state by selecting VM configuration and disks from various snapshots.
  • Support commit to the new state and undo to the previous one.
• Features based on specific disks snapshots, such as Storage Live Migration, will benefit from the new support
  • E.g. LSM will take a snapshot only on the migrated disks - as opposed to the current situation in which a snapshot is taken on all disks.

Detailed Description

Currently, a Snapshot represents a single point in time that contains the configuration of the VM and all attached disks.

I.e. creating/previewing/committing a snapshot must be done on the entire VM - including all the disks.

This feature introduces the ability to remove the constraint by allowing to exclude disks from a snapshot.

In addition, adds a new functionality of creating a customized snapshot composed of configuration and disk from multiple snapshots.

UI

Create Snapshot Dialog

Custom Preview Button

Custom Preivew Dialog

Screenshot

Video

Custom Preview Dialog - Video

REST-API

Add <disks> tag to create/restore snapshot.

Note: preview only is not available from rest (restore = preview + commit).

Create Snapshot:

POST /api/vms/{vm_id}/snapshots

<snapshot>
 <vm id="{vm_id}"/>
 <disks>
  <disk id="{disk_id}"/>
 </disks>
</snapshot>

Restore Snapshot:

POST /api/vms/{vm_id}/snapshots/{snapshot_id}/restore

<action>
 <restore_memory>"true|false"</restore_memory>
 <disks>
  <disk id="{disk_id}">
   <image_id>"{image_id}"</image_id>
   <snapshot id="{snapshot_id}"/>
  </disk>
 </disks>
</action>

oVirt 3.5

Preview Snapshot:

POST /api/vms/{vm_id}/preview_snapshot

<action>
 <snapshot id="{snapshot_id}"/>
 <restore_memory>`true|false`</restore_memory>
 <disks>
  <disk id="{disk_id}">
   <image_id>`{image_id}`</image_id>
   <snapshot id="{snapshot_id}"/>
  </disk>
 </disks>
</action>

Backend

• CreateAllSnapshotsFromVmCommand
  • The command should support handling a specified disks list.
  • Disks not included in specified list should be ‘fast-forwarded’ to active snapshot (i.e. update snapshot id without creating a new snapshot).
• TryBackToAllSnapshotsOfVmCommand
  • The command should support handling a specified disks list.
  • Ability to preview a subset of VM disks.
  • Allow previewing to various points of time (each specified image can define a different snapshot).
  • Support previewing only disks while keeping the current VM configuration.
  • Keeping old API from ‘regular’ preview.
• RestoreAllSnapshotsCommand
  • Identify on which disks to perform snapshot undo/commit.
  • Skip restore for excluded disks (but keep updating snapshot id accordingly).
• GetAllVmSnapshotsByVmIdQuery
  • Configurable support to return the snapshots with appropriate images list.
  • Fetch disks data from VM configuration which resides in the OVF (depending on UI design).
• Snapshot
  • Add a list of disk images.

VDSM

Already supported.

Open Issues

• Custom Preview Dialog
  • What to display at the bottom section?
    • “Result” - i.e. the state to preview.
    • VM configuration - i.e. the bottom section updates on configuration selection.
    • Decision: the bottom section displays the ‘result’ snapshot.
  • Memory (applicable only for live snapshot)
    • Should we allow configuration/memory decoupling?
    • Or, configuration selection enforces the selection of memory from same snapshot (and vice versa)?
    • Decision: VM configuration and memory are coupled. I.e. one cannot preview memory of a snapshot without selecting the same snapshot’s configuration.
  • Allow excluding a disk from preview (deselecting entire column)?
    • Excluding a disk implications are similar to deleting a disk (will result with an illegal disk on previous snapshots).
    • Decision: allow disk exclude for now.

Testing

• Verify that create snapshot flow has no regressions.
• Verify that the ‘regular’ preview/undo/commit flow has no regressions.
• Create a snapshot with a subset of disks.
• Custom preview a snapshot from various point of times.
• Undo/commit a custom previewed snapshot.

Future Work

• Revise error flows
  • E.g. failing to take a snapshot on one disk shouldn’t rollback the entire snapshot, instead, just exclude the disk from the snapshot.
• Continue the decoupling of snapshot components and use single disks snapshots when needed, as in LSM flow.
• Create a snapshot form disk context
  • Select a disk -> create snapshot (still requires including the VM configuration).
• Preview/commit/undo a snapshot from disk context
  • Only a subset of the disks at a time, since creating a preview snapshot locks most VM operations (adding/removing disks, etc).
• Exclude VM configuration
  • Do we want to allow creating a snapshot without VM configuration?
• Detach/Attach of disks with snapshots
  • How to represent/display snapshots of a floating disk?
  • How to handle attach of a disk with snapshots to a different VM?
• Profiles
  • Creating a snapshot profiles (which allows single click snapshot). E.g. ‘VM configuration + OS disk profile’ / etc.