[dm-crypt] LUKS is written to a device with no partition table. Is it possible to add a partition table?

f-dm-c at media.mit.edu f-dm-c at media.mit.edu
Wed Apr 20 04:28:17 CEST 2016

I know you don't want to throw hardware at the problem, but if your
data now fits in 4TB, I'd recommend that you buy a 4TB drive, put
LUKS on it, copy the data to it, reconfigure your 12TB RAID5, move
the data back to the RAID, and then return the drive, paying the
restocking fee.  Or sell it privately.  Unless your time is free
and your data is valueless, this seems the most straightforward
way to solve the problem.  Note that you need not wipe the returned
drive, since you put LUKS on it first, though if you want to be
super-paranoid, wipe the first few megabytes of it before return.

If you don't trust having your data on a single drive during the
process, buy two 4TB drives and copy twice.  Don't make them a RAID;
that just makes everything more complicated and more prone to failure
or mistakes.  Just make two copies and leave one copy on the shelf
while you copy back over your 12TB RAID.  Or, if you have backups of
your RAID already (you -do- have backups, right?  else you shouldn't
be considering your data safe even when you're -not- monkeying with
the RAID), then maybe a single 4TB copy is enough, assuming that you
have checked that your backups are actually backups and not something
you can't read or perhaps something that was never written.

And if you didn't have backups, then keep the drive(s), and now you do.

Since it's a RAID5, you -could- live more dangerously and fail enough
drive(s) to get 4TB of free drives out of it instead of buying new
drive(s), and then re-add the drive(s) when everything's done.  But
this raises the chances that something will go wrong and leave you
with a smoking crater instead of your data.

P.S.  And next time, don't scrimp on "wasting" a disk sector to avoid
having a partition table.  Don't even worry about "wasting" a possible
megabyte (default alignment) at the start of each partition.  Your
12TB RAID will never notice.  And this way, certain other software
(like installers) are less likely to believe that the disk is blank
and write something unfortunate to it, like a partition table in the
middle of your RAID or LUKS headers.

More information about the dm-crypt mailing list