How to identify the journal disk for a Ceph OSD?

In many cases, one would like to understand the journal disk a particular OSD is using. There are two methods to understand this:

a) This is the most direct method, and should give you details on the OSD disks and the corresponding journal disks.

# ceph-disk list

This should output something like:

# ceph-disk list
 /dev/sda :
  /dev/sda1 other, xfs, mounted on /boot
  /dev/sda2 other, LVM2_member
 /dev/sr0 other, unknown
 /dev/vda :
  /dev/vda1 ceph data, active, cluster ceph, osd.0, journal /dev/vda2
  /dev/vda2 ceph journal, for /dev/vda1
 /dev/vdb :
  /dev/vdb1 ceph data, active, cluster ceph, osd.1, journal /dev/vdc1
 /dev/vdc :
  /dev/vdc1 ceph journal, for /dev/vdb1

b) The second method is cruder, and involves listing the OSD mount point on the file system.

# ls -l /var/lib/ceph/osd/ceph-0/

total 52
 -rw-r--r--.  1 root root  191 Aug  3 18:02 activate.monmap
 -rw-r--r--.  1 root root    3 Aug  3 18:02 active
 -rw-r--r--.  1 root root   37 Aug  3 18:02 ceph_fsid
 drwxr-xr-x. 70 root root 4096 Aug  4 00:38 current
 -rw-r--r--.  1 root root   37 Aug  3 18:02 fsid
 lrwxrwxrwx.  1 root root   58 Aug  3 18:02 journal -> /dev/disk/by-partuuid/d9ebc4bd-7b5e-4e12-b909-0c72c4f58ee0
 -rw-r--r--.  1 root root   37 Aug  3 18:02 journal_uuid
 -rw-------.  1 root root   56 Aug  3 18:02 keyring
 -rw-r--r--.  1 root root   21 Aug  3 18:02 magic
 -rw-r--r--.  1 root root    6 Aug  3 18:02 ready
 -rw-r--r--.  1 root root    4 Aug  3 18:02 store_version
 -rw-r--r--.  1 root root   42 Aug  3 18:02 superblock
 -rw-r--r--.  1 root root    0 Aug  5 13:09 sysvinit
 -rw-r--r--.  1 root root    2 Aug  3 18:02 whoami

# ls -l /dev/disk/by-partuuid/d9ebc4bd-7b5e-4e12-b909-0c72c4f58ee0
 lrwxrwxrwx. 1 root root 10 Aug  5 13:08 /dev/disk/by-partuuid/d9ebc4bd-7b5e-4e12-b909-0c72c4f58ee0 -> ../../vda2

As you can see, the file ‘journal’ is a symlink to the journal disk. The first method is much easier, but its always better to know how things are layered out underneath.

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