* Ceph cluster with old nodes having 6TB HDDs * Add new node with new 12TB HDDs
Halving IOPS-per-TB? https://www.sabi.co.uk/blog/17-one.html?170610#170610 https://www.sabi.co.uk/blog/15-one.html?150329#150329
Is it supported/recommended to pack 2 6TB HDDs handled by 2 old OSDs into 1 12TB LVM disk handled by 1 new OSD ?
The OSDs are just random daemons, what matters to chunk distribution in Ceph is buckets, and in this case leaf buckets. So it all depends on the CRUSH map but I suspect that manipulating it so that two existing leaf buckets become one is not possible or too tricky to attempt. One option would be to divide the 12TB disk in 2 partitions/LVs of 6TB and run 2 OSDs against it. It is not recommended, but I don't see a big issue in this case other than IOPS-per-TB.