Ceph: How to specifiy DB device for Bluestore OSD

[Piers Dawson-Damer]

How to specify DB device (not WAL device) for Bluestore OSD?

The Proxmox documentation of pveceph (pve.proxmox.com/pve-docs/chapter-pveceph.html) clearly shows how to specify a WAL device, but not a DB device.

pveceph createosd /dev/sdn -wal_dev /dev/sdb

Having used this method, within the GUI, only the WAL device is located on a seperate SSD.

Screencap --> dropbox.com/s/38igpoe9bjxj739/ceph_how_to_specifiy_db_device_for_bluestore_os.png

It was my understanding that the best practice when the SSD/Journal device has ample space, is to use it as a DB device.

...
If there is only a small amount of fast storage available (e.g., less than a gigabyte), we recommend using it as a WAL device. If there is more, provisioning a DB device makes more sense. The BlueStore journal will always be placed on the fastest device available, so using a DB device will provide the same benefit that the WAL device would while also allowing additional metadata to be stored there (if it will fix).

A single-device BlueStore OSD can be provisioned with:

ceph-volume lvm prepare --bluestore --data <device>

To specify a WAL device and/or DB device,

ceph-volume lvm prepare --bluestore --data \<device\> --block.wal \<wal-device\> --block.db \<db-device\>​

via docs.ceph.com/docs/mimic/rados/configuration/bluestore-config-ref

 

[Alwin]

pveceph help createod
USAGE: pveceph createosd <dev> [OPTIONS]
  -journal_dev <string>

         Block device name for journal (filestore) or block.db
         (bluestore).

  -wal_dev   <string>

         Block device name for block.wal (bluestore only).

This is a point to improve on the docs.