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ha crs: document scheduling points and new ha-rebalance-on-start option
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
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@ -1017,14 +1017,14 @@ the service's group.
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NOTE: There are plans to add modes for (static and dynamic) load-balancing in
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NOTE: There are plans to add modes for (static and dynamic) load-balancing in
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the future.
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the future.
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Basic
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Basic Scheduler
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~~~~~
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~~~~~~~~~~~~~~~
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The number of active HA services on each node is used to choose a recovery node.
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The number of active HA services on each node is used to choose a recovery node.
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Non-HA-managed services are currently not counted.
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Non-HA-managed services are currently not counted.
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Static
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Static-Load Scheduler
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~~~~~~
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~~~~~~~~~~~~~~~~~~~~~
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IMPORTANT: The static mode is still a technology preview.
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IMPORTANT: The static mode is still a technology preview.
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@ -1045,6 +1045,34 @@ currently not recommended to use it if you have thousands of HA managed
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services.
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services.
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CRS Scheduling Points
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~~~~~~~~~~~~~~~~~~~~~
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The CRS algorithm is not applied for every service in every round, since this
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would mean a large number of constant migrations. Depending on the workload,
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this could put more strain on the cluster than could be avoided by constant
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balancing.
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That's why the {pve} HA manager favors keeping services on their current node.
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The CRS is currently used at the following scheduling points:
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- Service recovery (always active). When a node with active HA services fails,
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all its services need to be recovered to other nodes. The CRS algorithm will
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be used here to balance that recovery over the remaining nodes.
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- HA group config changes (always active). If a node is removed from a group,
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or its priority is reduced, the HA stack will use the CRS algorithm to find a
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new target node for the HA services in that group, matching the adapted
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priority constraints.
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- HA service stopped -> start transtion (opt-in). Requesting that a stopped
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service should be started is an good opportunity to check for the best suited
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node as per the CRS algorithm, as moving stopped services is cheaper to do
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than moving them started, especially if their disk volumes reside on shared
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storage. You can enable this by setting the **`ha-rebalance-on-start`**
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CRS option in the datacenter config. You can change that option also in the
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Web UI, under `Datacenter` -> `Options` -> `Cluster Resource Scheduling`.
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ifdef::manvolnum[]
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ifdef::manvolnum[]
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include::pve-copyright.adoc[]
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include::pve-copyright.adoc[]
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endif::manvolnum[]
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endif::manvolnum[]
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