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Document KVM volume live migration on Ceph RBD and between RBD and file-based pools #696

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Document KVM volume live migration on Ceph RBD and between RBD and file-based pools #696

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27 changes: 20 additions & 7 deletions source/adminguide/storage.rst
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Expand Up @@ -893,17 +893,30 @@ Migrating an Instance Volume to a New Storage Pool
(XenServer, VMware) You can live migrate an Instance's volumes from one
storage pool to another, without stopping the Instance first.

(KVM) KVM does not support volume live migration due to the limited possibility
to refresh VM XML domain. Therefore, to live migrate a volume between storage pools,
one must migrate the VM to a different host as well to force the VM XML domain update.
Use 'migrateVirtualMachineWithVolumes' instead or stop the Instance and then migrate
the volume.
(KVM) A volume of a running Instance can be live migrated, without stopping or moving
the Instance, between:

- two Ceph RBD primary storage pools;
- a Ceph RBD pool and an NFS, SharedMountPoint or local (host-scoped) pool, in both directions.

For a local pool, the pool must be the one of the host the Instance is running on, as the copy
runs on that host. The whole disk is copied, hence a volume created from a template does not
depend on the backing file of the source pool afterwards, and the source volume is removed once
the migration is completed. Encrypted volumes can be migrated between RBD and NFS pools, both
online and offline.

For any other pair of pools, such as two NFS pools, KVM does not support volume live migration
due to the limited possibility to refresh VM XML domain. Therefore, one must migrate the
Instance to a different host as well to force the VM XML domain update, using
'migrateVirtualMachineWithVolumes', or stop the Instance and then migrate the volume.
A volume which is not attached to a running Instance can be migrated between any of these pools.

#. Log in to the CloudStack UI as a user or admin.

#. In the left navigation bar, click Instances, and click the Instance name.

#. (KVM only) Stop the Instance.
#. (KVM only) Stop the Instance, unless the volume is migrated live between the
storage pools listed above.

#. Click the Migrate button |Migrateinstance.png| and choose the
destination from the dropdown list.
Expand All @@ -916,7 +929,7 @@ the volume.
#. Watch for the volume status to change to Migrating, then back to
Running (or Stopped, in the case of KVM). This can take some time.

#. (KVM only) Restart the Instance.
#. (KVM only) Restart the Instance, if it was stopped.

.. note::
In case of KVM and PowerFlex/ScaleIO storage, live migration of
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