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On a fresh hard disk, I created a GPT partition table with three partitions:

/dev/sdd1 256M for /boot
/dev/sdd2   8G for swap
/dev/sdd3  ~1T for /

Then, I accidently formatted the raw device /dev/sdd with BtrFS. I thought: no problem - fresh disk anyway. I recreated the partition table, prepared the swap space and now formatted /dev/sdd3 with BtrFS. The boot partition is not yet in use. When BtrFS proofs stable for me I will make that disk my primary boot disk and pool my former LVM volumes into the BtrFS pool - but that is not of matter now. I rsync'ed all my data partitions to subvolumes on the BtrFS partition, configured the kernel and grub and rebooted. All is fine, working, and: Wow, it's faster.

But everytime BtrFS progs are scanning for BtrFS volumes they still see the /dev/sdd volume which I accidently formatted before I redid partitioning. How do I fix it? It seems not to hurt now, but I don't want any utility try to fiddle around with /dev/sdd by accident just because it sees BtrFS there...

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I guess some Btrfs superblock mirrors are still there. They are expected to be at offset 64 KiB, 64 MiB, 256 GiB (and 1 PiB) from the block device start and begin with BTRFS_MAGIC ("_BHRfS_M"). Blanking these markers should fix the issue. Don't forget to backup your file system before attempting doing this !

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  • 4
    You made my day... Used VCHE to replace on of the magic bytes at around 64k - no it works. :-)
    – hurikhan77
    Oct 12, 2011 at 21:10

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