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[SOLVED] Phantom btrfs filesystem
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Alela
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Joined: 31 Dec 2012
Posts: 10

PostPosted: Sat Mar 01, 2014 5:25 pm    Post subject: [SOLVED] Phantom btrfs filesystem Reply with quote

Dear all,

I observe a mysterious phantom btrfs filesystem and I don't know how to remove it.

Code:

# btrfs fi show
failed to read /dev/sr0
Label: none  uuid: ec71d72e-b225-46eb-88b8-27e8237ec9ea
   Total devices 4 FS bytes used 28.00KB
   devid    3 size 1.36TB used 2.01GB path /dev/sdc
   devid    4 size 1.36TB used 2.01GB path /dev/sdd
   devid    2 size 1.36TB used 2.01GB path /dev/sdb
   devid    1 size 1.36TB used 2.03GB path /dev/sda

Btrfs v0.20-rc1


gdisk shows me an empty disk without partitions.

Code:

# gdisk /dev/sda
GPT fdisk (gdisk) version 0.8.5

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): p
Disk /dev/sda: 2930277168 sectors, 1.4 TiB
Logical sector size: 512 bytes
Disk identifier (GUID): 43E3BCB2-57A3-4F1C-B51E-0EE62E1059EC
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 2930277134
Partitions will be aligned on 2048-sector boundaries
Total free space is 2930277101 sectors (1.4 TiB)

Number  Start (sector)    End (sector)  Size       Code  Name



Gparted gives me the same results for the four drives.

So, the question is how to exorcise my system?


Last edited by Alela on Sat Mar 01, 2014 6:04 pm; edited 1 time in total
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Alela
n00b
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Joined: 31 Dec 2012
Posts: 10

PostPosted: Sat Mar 01, 2014 6:04 pm    Post subject: Reply with quote

Problem solved! I found the answer on the btrfs FAQ: https://btrfs.wiki.kernel.org/index.php/Problem_FAQ

The solution is to remove the superblocks magic strings from the devices:

Code:
# dd if=/dev/zero bs=1 count=8 of=/dev/sda seek=$((64*1024+64))
# dd if=/dev/zero bs=1 count=8 of=/dev/sda seek=$((64*1024*1024+64))
# dd if=/dev/zero bs=1 count=8 of=/dev/sda seek=$((256*1024*1024*1024+64))
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