[pve-devel] [PATCH docs 2/2] ceph: add explanation on the pg autoscaler

Dylan Whyte d.whyte at proxmox.com
Fri Jan 15 15:19:25 CET 2021


Sorry, I didn't prefix the other reply with a comment. Anyway, everything was pretty much fine, I just had some little issues. With this, I have some even more minor issues.

>     On 15.01.2021 14:17 Alwin Antreich <a.antreich at proxmox.com mailto:a.antreich at proxmox.com > wrote:
> 
> 
>     Signed-off-by: Alwin Antreich <a.antreich at proxmox.com mailto:a.antreich at proxmox.com >
>     ---
>     pveceph.adoc | 36 ++++++++++++++++++++++++++++++++++++
>     1 file changed, 36 insertions(+)
> 
>     diff --git a/pveceph.adoc b/pveceph.adoc
>     index 42dfb02..da8d35e 100644
>     --- a/pveceph.adoc
>     +++ b/pveceph.adoc
>     @@ -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 is too
>     +different from the current value.
> 
s/is too different/differs too much/
(note: "too different" seems grammatically correct but something sounds strange about it here. It could just be a personal thing..)

>     +on:: The `pg_num` is adjusted automatically with no need for any manual
>     +interaction.
>     +off:: No automatic `pg_num` adjustments are made, no warning will be issued
> 
s/made, no/made, and no/

>     +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
>     ---------------------------
>     --
>     2.29.2
> 
> 
> 
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