[ceph-users] How to use ceph-volume to create multiple OSDs per NVMe disk, and with fixed WAL/DB partition on another device?

I'm building a new 4-node Proxmox/Ceph cluster, to hold disk images for our VMs. (Ceph version is 15.2.5). Each node has 6 x NVMe SSDs (4TB), and 1 x Optane drive (960GB). CPU is AMD Rome 7442, so there should be plenty of CPU capacity to spare. My aim is to create 4 x OSDs per NVMe SSD (to make more effective use of the NVMe performance) and use the Optane drive to store the WAL/DB partition for each OSD. (I.e. total of 24 x 35GB WAL/DB partitions). However, I am struggling to get the right ceph-volume command to achieve this. Thanks to a very kind Redditor, I was able to get close: /dev/nvme0n1 is an Optane device (900GB). /dev/nvme2n1 is an Intel NVMe SSD (4TB). ``` # ceph-volume lvm batch --osds-per-device 4 /dev/nvme2n1 --db-devices /dev/nvme0n1 Total OSDs: 4 Solid State VG: Targets: block.db Total size: 893.00 GB Total LVs: 16 Size per LV: 223.25 GB Devices: /dev/nvme0n1 Type Path LV Size % of device ---------------------------------------------------------------------------------------------------- [data] /dev/nvme2n1 931.25 GB 25.0% [block.db] vg: vg/lv 223.25 GB 25% ---------------------------------------------------------------------------------------------------- [data] /dev/nvme2n1 931.25 GB 25.0% [block.db] vg: vg/lv 223.25 GB 25% ---------------------------------------------------------------------------------------------------- [data] /dev/nvme2n1 931.25 GB 25.0% [block.db] vg: vg/lv 223.25 GB 25% ---------------------------------------------------------------------------------------------------- [data] /dev/nvme2n1 931.25 GB 25.0% [block.db] vg: vg/lv 223.25 GB 25% --> The above OSDs would be created if the operation continues --> do you want to proceed? (yes/no) ``` This does split up the NVMe disk into 4 OSDs, and creates WAL/DB partition on the Optane drive - however, it creates 4 x 223 GB partitions on the Optane (whereas I want 35GB partitions). Is there any way to specify the WAL/DB partition size in the above? And can it be done, such that you can run successive ceph-volume commands, to add the OSDs and WAL/DB partitions for each NVMe disk? (Or if there's an easier way to achieve the above layout, please let me know). That being said - I also just saw this ceph-users thread: https://lists.ceph.io/hyperkitty/list/ceph-users@ceph.io/thread/3Y6DEJCF7ZM… It talks there about "osd op num shards" and "osd op num threads per shard" - is there some way to set those, to achieve similar performance to say, 4 x OSDs per NVMe drive, but with only 1 x NVMe? Has anybody done any testing/benchmarking on this they can share?