Unfortunately, this was recently IDed as a major weakness of the current MDS rank configuration system. :/ You can follow https://tracker.ceph.com/issues/75892 which was filed to work on this. -Greg On Tue, May 5, 2026 at 11:34 PM Robert Sander via ceph-users < ceph-users@ceph.io> wrote:

Hi,

Given a cluster with multiple racks or rooms where the rack or room is the failure domain for replicated pools.

Given one or more CephFS volumes (filesystems) with at least one active MDS each and a standby-replay for each active MDS.

Each room or rack contains multiple MDS daemons (one per host).

Is there a possibility to guarantee that the standby-replay MDS for each active MDS does not run in the same failure domain (rack or room)?

Because when both run in the same failure domain and that domain fails there is no point in having a standby-replay.

Are there any ideas on how to solve this?

Regards -- Robert Sander Linux Consultant

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