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ceph: add explanation on the pg autoscaler

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Signed-off-by: Alwin Antreich <a.antreich@proxmox.com>
Originally-by: Alwin Antreich <a.antreich@proxmox.com>
Edited-by: Dylan Whyte <d.whyte@proxmox.com>
Signed-off-by: Dylan Whyte <d.whyte@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
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Dylan Whyte 2021-02-18 11:39:10 +01:00 committed by Thomas Lamprecht
parent c446b6bbc7
commit 47d62c847c
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pveceph.adoc
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@ -540,6 +540,42 @@ pveceph pool destroy <name>
NOTE: Deleting the data of a pool is a background task and can take some time.
You will notice that the data usage in the cluster is decreasing.
PG Autoscaler
~~~~~~~~~~~~~
The PG autoscaler allows the cluster to consider the amount of (expected) data
stored in each pool and to choose the appropriate pg_num values automatically.
You may need to activate the PG autoscaler module before adjustments can take
effect.
[source,bash]
----
ceph mgr module enable pg_autoscaler
----
The autoscaler is configured on a per pool basis and has the following modes:
[horizontal]
warn:: A health warning is issued if the suggested `pg_num` value differs too
much from the current value.
on:: The `pg_num` is adjusted automatically with no need for any manual
interaction.
off:: No automatic `pg_num` adjustments are made, and no warning will be issued
if the PG count is far from optimal.
The scaling factor can be adjusted to facilitate future data storage, with the
`target_size`, `target_size_ratio` and the `pg_num_min` options.
WARNING: By default, the autoscaler considers tuning the PG count of a pool if
it is off by a factor of 3. This will lead to a considerable shift in data
placement and might introduce a high load on the cluster.
You can find a more in-depth introduction to the PG autoscaler on Ceph's Blog -
https://ceph.io/rados/new-in-nautilus-pg-merging-and-autotuning/[New in
Nautilus: PG merging and autotuning].
[[pve_ceph_device_classes]]
Ceph CRUSH & device classes
---------------------------