Examining the code, there are several sgdisk calls, but two are relevant
for this discussion. The first is the one reproduced in this initial bug
report:

sgdisk --zap-all --clear --mbrtogpt

This call does not seem to have been changed as a result of bug
#1257491. Upon further review, I think I see why it's written this way:
When "sgdisk --zap-all --clear" is fed an MBR disk, sgdisk wipes the
disk but then refuses to create a blank GPT because it still thinks it's
dealing with an MBR disk. This is a bug and I'll fix it soon. Adding
--mbrtogpt works around this bug and results in a blank GPT disk.

The call that bug #1257491 resulted in changing was elsewhere in the
script, from lines 840 to 856 at
http://ceph.com/git/?p=ceph.git;a=blob;f=src/ceph-
disk;h=f771a68c2f9d873710cbe380d702fd0baa725da9;hb=HEAD#l840:

sgdisk --new={part} --change-name={num}:ceph journal --partition-
guid={num}:{journal_uuid} --typecode={num}:{uuid} journal

It was to THIS call that --mbrtogpt was added, if I've backtracked it
correctly. Again, I don't understand the context, but my guess is that
sgdisk was being called on an MBR disk. By default, sgdisk will refuse
to write data to an MBR disk. This is a safety feature, in case it's
called carelessly on an MBR disk that should NOT be converted to GPT
form; but of course if a script doesn't know whether the input will be
GPT or MBR but the intent of the script is to write out a GPT disk,
having sgdisk convert the data structures makes sense, so --mbrtogpt
exists.

So in sum, sgdisk does have a bug, but it's not the one assumed. The
charm described here was written to work around the bug, and I believe
you've misinterpreted the expected output of the relevant sgdisk
command.

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https://bugs.launchpad.net/bugs/1303903

Title:
  sgdisk zap/clear doesn't wipe all GPT tables

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