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I would like to say this bug still persist on Debian Stretch.
I suggest this bug to be marked as 'critical', since this could lead to data loss.
The debian installer doesn't recognize a previous encrypted volume (Tested with netinstall.iso). The critical is that even with workaround to recognize the partitions on encrypted volume the installer only advances on formating these partitions causing data-loss.
This is a long time bug and I think this could be fixed in time for Stretch release. I don't know if the Ubuntu installer is the same but this bug doesn't exists on Ubuntu.
How to achieve the bug:
On "Partition disk" go to "Configure encrypted volumes"
Select "Create encrypted volume". This will make anna install the necessary packages to work with encryption.
P.s.: on Ubuntu, this step shows an option to setup an existing encrypted volume.
Do NOT save changes to disk.
Go back. Open a shell. Open luks volume. Activate volume group. Exit.
Detect disks. LVM partitions are now seen.
Step 7 (This is the critical bug):
Choosing any LVM partition and selecting to use as the previous format system leads to "re-format" the partition. This step should ask if you want to keep the existing file system. This could lead to /home data loss.
On Ubuntu you can choose to not format the partition at this stage.
I hope this help to solve this annoying problem. Today its impossible to install Debian on an already encrypted system without data loss.
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