- enable indexing (xtime marking) on a volume
- mount the vol with --client-pid=-1
- delete the timestamp file(s) (/etc/glusterd/vols/<volname>/marker.tstamp)
- see what you get when you query the xattr "trusted.glusterfs.volume-mark" on the mountpoint -- expected result is a blob of 27 octets the so that the octet at index 18 is 1; actually you get a blob of 27 octets which has the octet at index 18 being 0. (Alternative testing with gsyncd: use the volume as geo-rep master; expected behavior is to see gsyncd crash with message "master is corrupt".)

After fix provided, it's suggested to be verified on both single-brick setups (to test just marker's composition of the xattr in question) and on multi-node clustered setups where you just delete the timestamp file on some nodes (to test xattr aggregation).