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Host HA support on Ceph RBD primary storage for KVM #694

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Host HA support on Ceph RBD primary storage for KVM #694

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25 changes: 25 additions & 0 deletions source/adminguide/reliability.rst
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Expand Up @@ -190,6 +190,8 @@ that you want to dedicate to HA-enabled Instances.
a crash.


.. _ha-enabled-hosts:

HA-Enabled Hosts
----------------

Expand All @@ -208,6 +210,29 @@ Out of band management is a requirement of HA-Enabled hosts and has to be
configured on all intended participating hosts.
(see `“Out of band management” <hosts.html#out-of-band-management>`_).

Host-HA relies on a heartbeat and on a VM activity check of the host. The
supported primary storage types are NFS, SharedMountPoint, Ceph RBD, StorPool
and Linstor. Other primary storage types, such as PowerFlex/ScaleIO, SolidFire,
iSCSI and multipath SCSI, are not supported by Host-HA.

- NFS and SharedMountPoint: the heartbeat is a file on the mount point of the
storage pool, and the activity of an Instance is detected from the
modification time of its disk files.
- Ceph RBD: RBD has no mount point, so the KVM agent stores the heartbeat of
each host as a small RADOS object in the Ceph pool, and detects the activity
of an Instance through the watchers of its RBD images. The checks use the
Python bindings of Ceph, so the ``python3-rados`` and ``python3-rbd``
packages are required on the KVM hosts (they are dependencies of the
CloudStack agent package). The monitors, the pool and the cephx user and key
of the primary storage are used for these checks.
- StorPool: no heartbeat is written to the storage. The KVM agent checks with
the ``storpool`` command that the StorPool node of the host is running, and
uses the same check for the activity of the host.
- Linstor: no heartbeat is written to the storage. The KVM agent checks the
connections of the host with ``drbdsetup status`` and asks the Linstor
controller whether the node of the host is online, and uses the same check
for the activity of the host.

Host-HA has granular configuration on a host/cluster/zone level. In a large
environment, some hosts from a cluster can be HA-enabled and some not,

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