[ceph-users] Re: HDD replacements with shared NVME lvm for DB - what am I missing here

The NVME has nothing else other than the 14 LVM partitions (all created by ceph orch when it was originally deployed). So it's not empty now; it has the other 13 lvms on it for the other working OSDs, but it has ~50 GB left which won't ever get reused

Not strictly true. All SSDs have some degree of overprovisioning: physical NAND capacity that is not exposed to the host, but is used for sparing and other housekeeping. The difference between read-intensive and mixed-use SKUs is often simply that a greater percentage is thus reserved. So you can think of that 50GB as getting you longer endurance.