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Date: Fri, 20 Jun 2014 15:20:55 +0200
From: Milan Broz <gmazyland@gmail.com>
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Subject: Re: [dm-crypt] Cryptsetup-reencrypt failing with error with option
 --new reduce-device-size
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To: Abhrajyoti Kirtania <abhrajyoti@gmail.com>, dm-crypt@saout.de

On 06/20/2014 02:36 PM, Abhrajyoti Kirtania wrote:
> cryptsetup-reencrypt /dev/sda8 --new --reduce-device-size 1024

> Cannot wipe header on device /dev/loop0. if i pass --reduce-device-size as 1024.
> But if i pass this size as 4096 then getting the error as "Device /dev/loop0 is too small."

New LUKS device header needs more than 1024 or 4096 bytes - you need space for keyslots.
Try reduce device size by 4 Megabytes (and do not forget to reduce fs first):

cryptsetup-reencrypt /dev/sda8 --new --reduce-device-size 4M

and it should work.

I will probably add more descriptive error message here, it is really cryptic.

Milan