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Update docs about volume snapshots on KVM #423

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merged 4 commits into from
Jan 16, 2025
Merged

Update docs about volume snapshots on KVM #423

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3cf2c06
update docs about snapshots on kvm
Aug 16, 2024
a2dca83
fix link
Aug 16, 2024
d9ebde0
really fix the link
Aug 16, 2024
93caa93
update incremental snapshots table
Aug 16, 2024
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19 changes: 13 additions & 6 deletions source/adminguide/storage.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -1141,11 +1141,18 @@ is running, the global setting 'kvm.snapshot.enabled' must be set to 'True'.

The Volume Snapshot creation has changed in recent versions:

Under the hood, first, a full Instance Snapshot is taken - this means that during the taking of
the Instance Snapshot the Instance will be in the "Paused" state (while RAM memory is being written to the
QCOW2 file), which means that Instance will be unavailable from the Network point of view.
When the Instance Snapshot is created, Instance is unpaused/resumed, the single Volume Snapshot is exported
to the Secondary Storage, and then the Instance Snapshots is removed from the Instance.
When the VM is running, a disk-only VM snapshot is taken, exclusively for the volume in question.
If the VM is stopped, the volume will be converted (with qemu-img convert). The final storage location is
determined by the ``snapshot.backup.to.secondary`` configuration; if it is false the snapshot will be copied
to a different directory in the same primary storage as the volume; if it is true the snapshot will be copied
to the secondary storage. If the snapshot is being taken in a file-based storage (NFS, SharedMountPoint, Local),
it will be copied directly to its final storage location, according to the configuration.

Since 4.20.0.0, ACS supports incremental snapshots for the KVM hypervisor when using file-based storage (NFS, SharedMountPoint, Local),
to enable incremental snapshots the ``kvm.incremental.snapshot`` configuration must be enabled. Furthermore, in order to take incremental snapshots
the KVM host must have at least Libvirt version 7.6.0+ and qemu version 6.1+. The size of the snapshot chains
will be determined by the ``snapshot.delta.max`` configuration, which affects both KVM and XenServer snapshots.
More information on the incremental snapshot feature for KVM can be found in its `specification <https://github.com/apache/cloudstack/issues/8907>`_.


Automatic Snapshot Creation and Retention
Expand Down Expand Up @@ -1187,7 +1194,7 @@ incremental backups are supported, every N backup is a full backup.
+------------------------------+------------------+------------------+-----+
| | VMware vSphere | Citrix XenServer | KVM |
+==============================+==================+==================+=====+
| Support incremental backup | No | Yes | No |
| Support incremental backup | No | Yes | Yes |
+------------------------------+------------------+------------------+-----+

.. note::
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