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.
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# ceph-disk list
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This should output something like:
[sourcecode language="bash" gutter="false"]
# 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 [/sourcecode]
b) The second method is cruder, and involves listing the OSD mount point on the file system.
[sourcecode language="bash" gutter="false"]
# 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
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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.