I strongly recommend running 5 mons. Given how you phrase the above it seems as though you might mean 3 dedicated mon nodes? If so I’d still run 5 mons, add the mon cephadm host label to two of the OSD nodes.
Right now. only one mon is "active" and used all of the time. You would still run 5 mons anyway?
Are you conflating mons and mgrs? Mons form a quorum, you need more than half of them able to reach each other.
No.
So you’re running a total of 1 mon daemon?
I checked bluestore_min_alloc_size and indeed there is a 4K value set for all of them. Even on new ones.
Groovy. You checked with “ceph osd metadata”?
Yes. Should it be set to different size/value?
No. The default used to be 64 KiB; in the Octopus / Pacific era code improvements were made that allowed the defaults to change to 4 KiB. This is baked into each OSD, which is why I asked how I did: you can inject or set in central config or ceph.conf a value different from how a given OSD was built, but it doesn’t actually take effect. This is a subtlety often missed, in fact just last week I worked with a vendor doc team to correct their docs.
On Sun, 28 Dec 2025, 21:42 Anthony D'Atri, <anthony.datri@gmail.com> wrote:
I strongly recommend running 5 mons. Given how you phrase the above
it
seems as though you might mean 3 dedicated mon nodes? If so I’d still run 5 mons, add the mon cephadm host label to two of the OSD nodes.
Right now. only one mon is "active" and used all of the time. You would still run 5 mons anyway?
Are you conflating mons and mgrs? Mons form a quorum, you need more than half of them able to reach each other.
No.
So you’re running a total of 1 mon daemon?
No, 3 mons.
participants (2)
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Anthony D'Atri
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Rok Jaklič