Re-adding disk to volume

Ah, it seems cryptsetup was run automatically. /dev/mapper/data-0 points to /dev/dm-0.

root@MyNAS:~# mount /dev/dm-0 /data
mount: wrong fs type, bad option, bad superblock on /dev/mapper/data-0,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.
root@MyNAS:~# dmesg | tail
[ 3169.231414] UBIFS (ubi0:0): un-mount UBI device 0
[ 3169.474448] NFSD: Using /var/lib/nfs/v4recovery as the NFSv4 state recovery directory
[ 3169.474888] NFSD: starting 90-second grace period (net c097fc40)
[ 3173.890476] BTRFS: device label 0e35246e:data devid 1 transid 558760 /dev/dm-0
[ 3174.259285] BTRFS (device dm-0): parent transid verify failed on 2474687627264 wanted 558760 found 558769
[ 3174.266676] BTRFS (device dm-0): parent transid verify failed on 2474687627264 wanted 558760 found 558769
[ 3174.290469] BTRFS: open_ctree failed
[ 3487.554478] BTRFS (device dm-0): parent transid verify failed on 2474687627264 wanted 558760 found 558769
[ 3487.556355] BTRFS (device dm-0): parent transid verify failed on 2474687627264 wanted 558760 found 558769
[ 3487.580507] BTRFS: open_ctree failed

So it seems that BTRFS is f*cked. I'll try to google for solutions later, see if I can save it.