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Snapshot & Backup — Pre-ACS 4.20

This page covers the CMP automated snapshot/backup feature used with CloudStack versions before 4.20. For ACS 4.20+, see CloudStack Native Backup (v4.20+).

Volume snapshots​

A volume snapshot is a point-in-time capture of an instance's disk (root or data volumes). It does not capture CPU or memory state.

  • Snapshots can be taken for both root disks and data disks
  • Taking snapshots of a running VM's root disk is disabled by default in recent CloudStack versions
  • To enable: set kvm.snapshot.enabled = true in CloudStack Global Settings

⚠️ If you use CMP Backup (Automated Snapshots) and VM snapshots are not working, enabling kvm.snapshot.enabled = true is mandatory.

Supported hypervisors: XenServer, VMware vSphere, KVM
Not supported: Oracle VM (OVM)

Restoring a volume snapshot​

OptionDescription
Create Volume from SnapshotMount restored volume to recover specific files
Create Template from SnapshotBoot a new instance from the template (root disk only)
Revert to SnapshotDirectly revert volume to snapshot state (storage/hypervisor dependent)

VM / Instance snapshots​

A VM snapshot captures the complete state of an instance including all data volumes and optionally CPU/memory state.

  • Memory capture supported only on NFS storage
  • For all other storage types, snapshot with memory will fail

Limitations​

  • Supported on: VMware, XenServer, KVM (NFS only)
  • Cannot attach or delete volumes when stored snapshots exist — delete all snapshots first
  • Service offering changes discard memory-included snapshots automatically
  • Cannot take VM and volume snapshots simultaneously on the same instance

Reference: https://docs.cloudstack.apache.org/en/4.20.1.0/adminguide/virtual\_machines.html#instance-snapshots

CMP automated backup (scheduled snapshots)​

CMP Backup is a scheduled/automated snapshot feature built on top of CloudStack's native snapshot capabilities.

How CMP chooses snapshot type​

ScenarioCMP behaviour
VM snapshots work on running VMUses VM snapshots with memory by default
VM snapshots do NOT work on running VMSet VM snapshot = NO in CMP setup; CMP falls back to root volume snapshot

Snapshot retention​

  • Each schedule specifies how many recurring snapshots to retain
  • Oldest snapshots are automatically deleted when the limit is exceeded
  • Currently managed via global settings; per-policy retention is on the roadmap

Backup billing​

  • Billed hourly based on VM storage size
  • Rate: hourly_rate × storage_GB
  • Example: 0.1/GB/hour × 50 GB = 5/hour
  • Billing starts when backup is enabled; stops immediately when disabled
  • All snapshots are deleted when backup is disabled

Backup limits​

Set backup_limit in global settings to control maximum snapshots retained per VM. When the limit is reached, the oldest snapshot is deleted to make room.

Restrictions​

  • Only one backup service per VM at a time
  • Disabling backup stops billing and deletes all associated snapshots immediately