migration to bigger disk

[Julius Niezufus]

I've got an 8 TB HDD, and I want to migrate all the content to a 10 TB disk.
The disk contains a Hidden Volume and the additional 2 TB on the new disk should be used to enlarge the hidden volume? What's the best way to migrate all the contents without decrypting the volumes? Both volumes only contain ordinary files, there is no OS on either volume.

[Gary Marks]

Hi Julius,

Migrating data from your 8TB disk to the new 10TB disk should be pretty straightforward once you set up your new partitions. The new hidden partition is limited to no more than the largest contiguous block of unused sectors at the end of the encrypted outer partition on the new drive, so you'll want to set up the hidden partition before copying files to the outer partition. Any files in the outer partition occupying space near the end would limit the size of the hidden partition that must also be located at the end. More info can be found here...
https://www.veracrypt.jp/en/Hidden%20Volume.html

Since you already have experience using a hidden volume, mounting an outer volume in a way that protects the inner hidden volume should already be part of your standard procedure. Anyone reading this not familiar can find that crucial information here...
https://www.veracrypt.jp/en/Protection%20of%20Hidden%20Volumes.html

Once your hidden partition is set up on the new disk and mounted, migrating data to it is just a matter of mounting your old hidden volume and copying the files. No decryption is required other than the on-the-fly decryption that comes with mounting the volume with VeraCrypt, and the same goes with the outer volume. Just be sure to always mount the outer volume so that the hidden volume is protected from overwriting. I suspect a lot of hidden volumes have been lost through this oversight.

[Julius Niezufus]

Okay, that's not really the answer I hoped for, as I've already started to mirror the disk. Is there no way to enlarge the hidden volume once it's already there? After all, when the mirroring process is done, there's plenty of unused space at the end of the disk.

[Gary Marks]

I wouldn't expect it to work, Julius, and certainly haven't tried it myself. If you finish the mirroring process you're currently performing, you'll be in possession of two complete copies of your data and you can test it for yourself, or you can set up a much smaller test to get a quicker answer that doesn't risk ruining a very large amount of data. I do know that the only reliable means to expand an encrypted volume is the built-in VeraCrypt Volume Expander available on the drop-down Tools menu. It only works correctly on NTFS formatted volumes and expressly warns against use on an outer volume that contains a hidden volume. You may get a more specific targeted warning if you attempt to expand a hidden volume.

[Julius Niezufus]

Something unexpected happened: After the mirroring completed, I tried to mount the volumes. Mounting the visible volume worked fine, but when I tried to mount the hidden volume (in Windows) I was asked to format the partition. Any ideas what went wrong here?

[Gary Marks]

I thought your mirroring would have worked, assuming it was done sector-by-sector, but it's probably not such a bad thing that it didn't. You'd still be stuck with the unresizable hidden volume smaller than you want, and the only way (I think) to fix it would be to start over and create your partitions from scratch (both outer and hidden) in your desired sizes. Then just copy the files to their respective volumes instead of using mirroring software. I didn't bother explaining why I think hidden volumes are unresizable, but I should have. It's my understanding that the VeraCrypt Volume Expander only expands a volume toward the end of the disk, never toward the front. Hidden volumes are already at the very end of the outer containing volume, so there's never any space available for resizing. There may be other technical reasons as well, but that seems the most obvious to me. Every aspect of hidden volumes is designed to evade detection of their existence for plausible deniability, and that imposes unusual restrictions on their use and also on the outer decoy volume that contains them.

[RealTehreal]

You cannot resize a VC volume the way you would do so with an unencrypted partition. VC volumes consist of your encrypted user data and quite a bunch of meta data. You would have to manipulate the meta data in a way, VC would use the remaining space on your media. Afterwards you would have to mount the volume without mounting the filesystem inside of it, resize that one as well, and hope that nothing bad happens. This would be quite error prone.

Therefore, you should setup your new media device with a new VC volume, mount both the new and the old VC volumes and copy over your user data. Easy, straight forwards, without tinkering.

Greets

Edit: I forgot: VC volumes have backup header (again: meta data) at the end of every volume. So, this data would have to be moved to the end of the new media as well. That would be quite a bit of tinkering...