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Re: How to make btrfs forget a disk?



Victor Sudakov wrote:
> 
> btrfs thinks that /dev/nvme1n1 has a btrfs:
> 
> # btrfs filesystem show
> Label: none  uuid: 3414ae53-f3d4-43ea-bb88-ffefc9bc86f6
>         Total devices 1 FS bytes used 1.05TiB
>         devid    1 size 2.00TiB used 1.33TiB path /dev/nvme0n1
> 
> Label: none  uuid: 38f74bc8-465d-4866-8ec1-3a144741012c
>         Total devices 1 FS bytes used 831.16GiB
>         devid    1 size 3.00TiB used 1.48TiB path /dev/nvme1n1
> 
> The problem is that /dev/nvme1n1 is being used for ZFS now, and there is
> currently no btrfs thereon. However, there is a btrfs label or something
> stuck somewhere, how can I clear it?
> 
> I tried to unload/load the btrfs kernel module but it did not help. 
> It's somewhere on disk, but where?

Found some hints and recipes in
https://btrfs.wiki.kernel.org/index.php/Problem_FAQ#How_to_clean_up_old_superblock_.3F
So the culprit probably *was* the btrfs superblock. Deloptes you were
right.

It's interesting however that "zpool create" created a GPT (which I did
not want), but did not erase a superblock from a previous filesystem.

A lesson? Always dd the first several MB of a disk with zeroes when
changing partitioning schemes, whole disk filesystems etc.

-- 
Victor Sudakov VAS4-RIPE
http://vas.tomsk.ru/
2:5005/49@fidonet

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