6. Keep one replica until three hosts have OSDs¶

Date: 2026-10-13

Status¶

Accepted

Context¶

Ceph pools default to size=3 and min_size=2. A placement group with fewer than min_size copies stops serving I/O, so with one OSD no I/O is possible under the defaults. Setting size=1 requires mon_allow_pool_size_one.

Decision¶

We'll set mon_allow_pool_size_one and run pools at size=1, min_size=1 until three hosts have OSDs. At that point we move them to size=3, min_size=2, with each copy on a different host.

Consequences¶

We can switch to size=3 later without downtime.