Hi,
My cluster is showing this warning
[WRN] MANY_OBJECTS_PER_PG: 1 pools have many more objects per pg than average
pool volumes_cache objects per pg (34082) is more than 10.0448
times cluster average (3393)
Thanks and Regards
Vishnu Bhaskar
Acceleron Labs Pvt Ltd
Bangalore, India
On Wed, Aug 13, 2025 at 1:35 PM Anthony D'Atri <a...@dreamsnake.net> wrote:
> Cache tiers are deprecated, I strongly advise finding a way to factor it
> out of your deployment.
>
> There was some discussion of this in the past, e.g.
>
> https://ceph-users.ceph.narkive.com/0LxBSHEQ/changing-pg-num-on-cache-pool
>
> The PG to RADOS object ratio isn't necessarily in and of itself a problem,
> as the dynamics of pg_num for a pool depend on the data and the access
> modality. When multiple pools share the same OSDs, there are tradeoffs
> that include what the pools are for, and how much data each stores. RGW
> index pools, for example, need more PGs than their data volume would
> otherwise indicate.
>
> Is your cache pool for sure limited to *only* the SSDs you expect, or does
> it specify a CRUSH rule that also lands on HDDs?
>
> -- the former Cepher known as Anthony
>
> On Aug 13, 2025, at 12:15 AM, Vishnu Bhaskar <vishn...@acceleronlabs.com>
> wrote:
>
> Hi Team,
>
> I have an OpenStack Ceph cluster where the Cinder volumes pool uses a cache
> pool named *volumes_cache*.
>
> Due to performance issues, I observed that the cache pool has fewer PGs and
> a high PG-to-object ratio, approximately 10x higher than normal. For
> instance, one PG contains around 35,000 objects. I am planning to increase
> the PG number for the cache pool.
>
> For the base pool, I was able to increase the PG count without any issues.
> However, for the cache pool, I encountered a warning indicating that a
> force argument is required. In my lab environment, I found that changing
> the cache pool mode to *none* allowed me to modify the PG number.
>
> Since this is my production setup, I would like to know if there is a safe
> and recommended procedure to increase the PG number of a *cache pool*
> without impacting the environment.
>
> Kindly advise on the best approach.
>
> Thanks and Regards
> Vishnu Bhaskar
> Acceleron Labs Pvt Ltd
> Bangalore, India
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