Comment 1 for bug 1475247

I had the same thing happen to a run of mine once:

2015-07-01 14:26:50 INFO mon-relation-changed ^GCaution: invalid backup GPT header, but valid main header; regenerating
2015-07-01 14:26:50 INFO mon-relation-changed backup header from main header.
2015-07-01 14:26:50 INFO mon-relation-changed
2015-07-01 14:26:50 INFO mon-relation-changed Warning! Main and backup partition tables differ! Use the 'c' and 'e' options
2015-07-01 14:26:50 INFO mon-relation-changed on the recovery & transformation menu to examine the two tables.
2015-07-01 14:26:50 INFO mon-relation-changed
2015-07-01 14:26:50 INFO mon-relation-changed Warning! One or more CRCs don't match. You should repair the disk!
2015-07-01 14:26:50 INFO mon-relation-changed

  16841 ? Ssl 0:00 /var/lib/juju/tools/unit-ceph-1/jujud unit --data-dir /var/lib/juju --unit-name ceph/1 --debug
  36054 ? S 0:02 \_ /usr/bin/python /var/lib/juju/agents/unit-ceph-1/charm/hooks/mon-relation-changed
  38589 ? S 0:00 \_ /bin/sh /usr/sbin/ceph-disk-prepare --fs-type xfs --zap-disk /dev/sdb
  38592 ? S 0:00 \_ /usr/bin/python /usr/sbin/ceph-disk prepare --fs-type xfs --zap-disk /dev/sdb
  38601 ? D 0:00 \_ /sbin/sgdisk --zap-all --clear --mbrtogpt -- /dev/sdb

It was stuck like this for hours. Nothing interesting in dmesg.

Since I was debugging potentially hardware disk issues on that node, I dismissed it.