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new 217a01d Update docs about volume snapshots on KVM (#423)
217a01d is described below
commit 217a01dff68bec069edc360d8d38779b3a820e4f
Author: João Jandre <[email protected]>
AuthorDate: Thu Jan 16 07:27:31 2025 -0300
Update docs about volume snapshots on KVM (#423)
Co-authored-by: João Jandre <[email protected]>
---
source/adminguide/storage.rst | 19 +++++++++++++------
1 file changed, 13 insertions(+), 6 deletions(-)
diff --git a/source/adminguide/storage.rst b/source/adminguide/storage.rst
index a2e7e3a..07f8f9b 100644
--- a/source/adminguide/storage.rst
+++ b/source/adminguide/storage.rst
@@ -1287,11 +1287,18 @@ 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
@@ -1333,7 +1340,7 @@ 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::
