BTRFS-SELECT-SUPER(8)                      Btrfs Manual                     BTRFS-SELECT-SUPER(8)

NAME
       btrfs-select-super - overwrite primary superblock with a backup copy

SYNOPSIS
       btrfs-select-super -s number <device>

DESCRIPTION
       Destructively overwrite all copies of the superblock with a specified copy. This helps in
       certain cases, for example when write barriers were disabled during a power failure and
       not all superblocks were written, or if the primary superblock is damaged, eg.
       accidentally overwritten.

       The filesystem specified by device must not be mounted.

           Note
           Prior to overwriting the primary superblock, please make sure that the backup copies
           are valid!

       To dump a superblock use the btrfs inspect-internal dump-super command.

       Then run the check (in the non-repair mode) using the command btrfs check -s where -s
       specifies the superblock copy to use.

       Superblock copies exist in the following offsets on the device:

       •   primary: 64KiB (65536)

       •   1st copy: 64MiB (67108864)

       •   2nd copy: 256GiB (274877906944)

       A superblock size is 4KiB (4096).

OPTIONS
       -s|--super <superblock>
           use 'superblock’th superblock copy, valid values are 0 1 or 2 if the respective
           superblock offset is within the device size

SEE ALSO
       btrfs-inspect-internal(8), btrfsck check(8)

Btrfs v4.20.1                               01/23/2019                      BTRFS-SELECT-SUPER(8)

usage: btrfs-map-logical [options] device
        -l Logical extent to map
        -c Copy of the extent to read (usually 1 or 2)
        -o Output file to hold the extent
        -b Number of bytes to read