[PATCH pve-docs 1/1] ceph: add warning about mixing device-specific with device-unspecific CRUSH rules when using autoscaler

[PATCH pve-docs 1/1] ceph: add warning about mixing device-specific with device-unspecific CRUSH rules when using autoscaler

[Nicolas Frey]

Suggested-by: Friedrich Weber <f.weber@proxmox.com>
Signed-off-by: Nicolas Frey <n.frey@proxmox.com>
---
 pveceph.adoc | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/pveceph.adoc b/pveceph.adoc
index 2aae6d6..dfa5d95 100644
--- a/pveceph.adoc
+++ b/pveceph.adoc
@@ -916,6 +916,9 @@ TIP: If the pool already contains objects, these must be moved accordingly.
 Depending on your setup, this may introduce a big performance impact on your
 cluster. As an alternative, you can create a new pool and move disks separately.

+WARNING: When using the autoscaler, all pools must either exclusively be assigned
+device-specific or device-unspecific CRUSH rules. Mixing them across pools will
+prevent the autoscaler from functioning.

 Ceph Client
 -----------
--
2.47.3

Re: [PATCH pve-docs 1/1] ceph: add warning about mixing device-specific with device-unspecific CRUSH rules when using autoscaler

[Kefu Chai]

Nicolas Frey <n.frey@proxmox.com> writes:

Hi Nicolas, thanks for this improvement. A few nits:

> Suggested-by: Friedrich Weber <f.weber@proxmox.com>
> Signed-off-by: Nicolas Frey <n.frey@proxmox.com>
> ---
>  pveceph.adoc | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/pveceph.adoc b/pveceph.adoc
> index 2aae6d6..dfa5d95 100644
> --- a/pveceph.adoc
> +++ b/pveceph.adoc
> @@ -916,6 +916,9 @@ TIP: If the pool already contains objects, these must be moved accordingly.
>  Depending on your setup, this may introduce a big performance impact on your
>  cluster. As an alternative, you can create a new pool and move disks separately.
>
> +WARNING: When using the autoscaler, all pools must either exclusively be assigned
> +device-specific or device-unspecific CRUSH rules. Mixing them across pools will
>

device-specific / device-unspecific is not Ceph's terminology. Ceph's
terms are "CRUSH rules that specify a device class", or simply "device
class rules".

> +prevent the autoscaler from functioning.

this might overstates the problem caused by overlapped roots. The
autoscaler keeps running: it just skips pools whose CRUSH rules's OSD
sets overlap, and the pg_num is not adjustted for those pools. In other
words, non-overlapping pools continue to scale.

So, probably we can be more specific here? like:

When using the PG autoscaler, all pools in the cluster must use
CRUSH rules of the same kind, either all specifying a device class,
or all without one. Otherwise the autoscaler will skip the affected
pools and their `pg_num` will not be adjusted.

what do you think?

>
>  Ceph Client
>  -----------
> --
> 2.47.3

Re: [PATCH pve-docs 1/1] ceph: add warning about mixing device-specific with device-unspecific CRUSH rules when using autoscaler

[Nicolas Frey]

On 4/22/26 8:23 AM, Kefu Chai wrote:
> Nicolas Frey <n.frey@proxmox.com> writes:
> 
> Hi Nicolas, thanks for this improvement. A few nits:
> 
>> Suggested-by: Friedrich Weber <f.weber@proxmox.com>
>> Signed-off-by: Nicolas Frey <n.frey@proxmox.com>
>> ---
>>  pveceph.adoc | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/pveceph.adoc b/pveceph.adoc
>> index 2aae6d6..dfa5d95 100644
>> --- a/pveceph.adoc
>> +++ b/pveceph.adoc
>> @@ -916,6 +916,9 @@ TIP: If the pool already contains objects, these must be moved accordingly.
>>  Depending on your setup, this may introduce a big performance impact on your
>>  cluster. As an alternative, you can create a new pool and move disks separately.
>>
>> +WARNING: When using the autoscaler, all pools must either exclusively be assigned
>> +device-specific or device-unspecific CRUSH rules. Mixing them across pools will
>>
> 
> device-specific / device-unspecific is not Ceph's terminology. Ceph's
> terms are "CRUSH rules that specify a device class", or simply "device
> class rules".
> 

Thanks! I was not aware of the terminology used by ceph here

>> +prevent the autoscaler from functioning.
> 
> this might overstates the problem caused by overlapped roots. The
> autoscaler keeps running: it just skips pools whose CRUSH rules's OSD
> sets overlap, and the pg_num is not adjustted for those pools. In other
> words, non-overlapping pools continue to scale.

Ah, thanks for the explanation!

> 
> So, probably we can be more specific here? like:
> 
> When using the PG autoscaler, all pools in the cluster must use
> CRUSH rules of the same kind, either all specifying a device class,
> or all without one. Otherwise the autoscaler will skip the affected
> pools and their `pg_num` will not be adjusted.
> 
> what do you think?
> 

That sounds great! I'll send a v2 with your suggestions

>>
>>  Ceph Client
>>  -----------
>> --
>> 2.47.3

superseded: [PATCH pve-docs 1/1] ceph: add warning about mixing device-specific with device-unspecific CRUSH rules when using autoscaler

[Nicolas Frey]

superseded-by:https://lore.proxmox.com/pve-devel/20260422075440.20996-1-n.frey@proxmox.com/T/#u