Le 26 June 2012 ? 00:49, David Sterba a écrit:

On Mon, Jun 25, 2012 at 11:54:50PM +0400, Dmitry MiksIr wrote:

quoted

Hello!
Long time ago I created btrfs on /dev/sda
After some changes btrfs moved to /dev/sda1 (well, to md, and sda1 is part
of md).

As result, <btrfs fi show> show me 2 filesystems: new one and old one.
Probably I need to do some cleaning. Can someone tell me what to do.

quick aid is to run this command:

dd if=/dev/zero of=/dev/sda bs=1k count=4 seek=64

(deletes just the btrfs superblock and will not touch anything
else)

Updated the wiki: 
https://btrfs.wiki.kernel.org/index.php/Problem_FAQ#How_to_clean_up_old_superblock_.3F

-- 
Xavier Nicollet