Simple trick to analyse the write patterns applied to your Ceph journal.

Assuming your journal device is /dev/sdb1, checking for 10 seconds:

$ iostat -dmx /dev/sbd1 10 | awk '/[0-9]/ {print $8}'
16.25

Now converting sectors to KiB.

16.25 * 512 / 1024 = 8

And yes, I was sending 8K requests :).

Here we rely on the avgrq-sz column from iostat.