[dm-crypt] moving/resizing a dm-crypt partition

Matthias Schniedermeyer ms at citd.de
Fri Jan 31 11:17:09 CET 2014

On 31.01.2014 10:42, Louis-David Mitterrand wrote:
> On Thu, Jan 30, 2014 at 07:50:10PM +0100, Matthias Schniedermeyer wrote:
> > 
> > As it is BTRFS, just create a second dm-crypt volume and add that to the 
> > existing BTRFS. As BTRFS can span several physical volumes, creating one 
> > big partition isn't strictly necessary.
> > If you use the same password and have "luck" that your dm-crypt 
> > setup-script in initrd/initramsfs opens both dm-crypt devices in one 
> > go, there shouldn't even be any discomfort by that solution.
> Hi,
> This is an interesting solution, I didn't know about btrfs's spanning
> capabilities.

BTRFS is like ZFS in that regard, it supports what someone described as: 
"blatant layering violations".

But that has also some nice site-effects. You can for e.g. set 
RAID-level either per subvolume (BTRFS has it's own LVM implementation) 
or down to per file. I'm not quite sure what it was (or will be).
And that can be changed at run-time and BTRFS will perform the necessary 
"rebalancing" to achieve want you told it you wanted (either now or in 
the future).

And if you ever read the description of Microsoft's latest filesystem 
"ReFS" you feel like reading a description of the feature-set of BTRFS 
or ZFS.

> As you point out the key is having initrd unlock both partitions and I'm
> not sure how to do it. So in the end I chose the "hard" solution of
> merging both partitions (with a backup), which went well.

Which is the better solution, less "historic cruft" to drag around.



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