linux:/home/linux # btrfs-show-super -a /dev/mapper/loop1p3 superblock: bytenr=65536, device=/dev/mapper/loop1p3 --------------------------------------------------------- csum 0x99139f9f [match] bytenr 65536 flags 0x1 magic _BHRfS_M [match] fsid 1af256b5-b1ad-443b-aeee-a6853e70b7e2 label generation 663595 root 1015238656 sys_array_size 226 chunk_root_generation 92016 root_level 1 chunk_root 20971520 chunk_root_level 1 log_root 0 log_root_transid 0 log_root_level 0 total_bytes 247739711488 bytes_used 184550191104 sectorsize 4096 nodesize 4096 leafsize 4096 stripesize 4096 root_dir 6 num_devices 1 compat_flags 0x0 compat_ro_flags 0x0 incompat_flags 0x1 csum_type 0 csum_size 4 cache_generation 663595 uuid_tree_generation 663595 dev_item.uuid 9daef36b-5a51-4fe9-b9fe-eb7036e52bb9 dev_item.fsid 1af256b5-b1ad-443b-aeee-a6853e70b7e2 [match] dev_item.type 0 dev_item.total_bytes 247739711488 dev_item.bytes_used 247739711488 dev_item.io_align 4096 dev_item.io_width 4096 dev_item.sector_size 4096 dev_item.devid 1 dev_item.dev_group 0 dev_item.seek_speed 0 dev_item.bandwidth 0 dev_item.generation 0 superblock: bytenr=67108864, device=/dev/mapper/loop1p3 --------------------------------------------------------- csum 0x3972b751 [match] bytenr 67108864 flags 0x1 magic _BHRfS_M [match] fsid 1af256b5-b1ad-443b-aeee-a6853e70b7e2 label generation 663595 root 1015238656 sys_array_size 226 chunk_root_generation 92016 root_level 1 chunk_root 20971520 chunk_root_level 1 log_root 0 log_root_transid 0 log_root_level 0 total_bytes 247739711488 bytes_used 184550191104 sectorsize 4096 nodesize 4096 leafsize 4096 stripesize 4096 root_dir 6 num_devices 1 compat_flags 0x0 compat_ro_flags 0x0 incompat_flags 0x1 csum_type 0 csum_size 4 cache_generation 663595 uuid_tree_generation 663595 dev_item.uuid 9daef36b-5a51-4fe9-b9fe-eb7036e52bb9 dev_item.fsid 1af256b5-b1ad-443b-aeee-a6853e70b7e2 [match] dev_item.type 0 dev_item.total_bytes 247739711488 dev_item.bytes_used 247739711488 dev_item.io_align 4096 dev_item.io_width 4096 dev_item.sector_size 4096 dev_item.devid 1 dev_item.dev_group 0 dev_item.seek_speed 0 dev_item.bandwidth 0 dev_item.generation 0 p1p3.fs_imageinux # btrfs-image -c 9 -t 8 /dev/mapper/loop1p3 /mnt/INTENSO-1/loo Check tree block failed, want=1015238656, have=0 Check tree block failed, want=1015238656, have=0 Check tree block failed, want=1015238656, have=0 Check tree block failed, want=1015238656, have=0 Check tree block failed, want=1015238656, have=0 read block failed check_tree_block Couldn't read tree root Open ctree failed create failed (Success) linux:/home/linux # btrfs-debug-tree /dev/mapper/loop1p3 Check tree block failed, want=1015238656, have=0 Check tree block failed, want=1015238656, have=0 Check tree block failed, want=1015238656, have=0 Check tree block failed, want=1015238656, have=0 Check tree block failed, want=1015238656, have=0 read block failed check_tree_block Couldn't read tree root unable to open /dev/mapper/loop1p3 linux:/home/linux # mount -o recovery,ro /dev/mapper/loop1p3 /mnt/btrfs mount: wrong fs type, bad option, bad superblock on /dev/mapper/loop1p3, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so. linux:/home/linux # journalctl | sed -n '/Oct 27 12:30:37/,$p' Oct 27 12:30:37 linux.site kernel: BTRFS info (device dm-2): enabling auto recovery Oct 27 12:30:42 linux.site kernel: BTRFS info (device dm-2): disk space caching is enabled Oct 27 12:30:42 linux.site kernel: BTRFS: bad tree block start 0 1015238656 Oct 27 12:30:42 linux.site kernel: BTRFS: bad tree block start 0 1015238656 Oct 27 12:30:42 linux.site kernel: BTRFS: failed to read tree root on dm-2 Oct 27 12:30:42 linux.site kernel: BTRFS: bad tree block start 0 1015238656 Oct 27 12:30:42 linux.site kernel: BTRFS: bad tree block start 0 1015238656 Oct 27 12:30:42 linux.site kernel: BTRFS: failed to read tree root on dm-2 Oct 27 12:30:46 linux.site kernel: parent transid verify failed on 1013854208 wanted 663594 found 663596 Oct 27 12:30:46 linux.site kernel: parent transid verify failed on 1013854208 wanted 663594 found 663596 Oct 27 12:30:46 linux.site kernel: BTRFS: failed to read tree root on dm-2 Oct 27 12:30:46 linux.site kernel: BTRFS: bad tree block start 0 1015197696 Oct 27 12:30:46 linux.site kernel: BTRFS: bad tree block start 0 1015197696 Oct 27 12:30:46 linux.site kernel: BTRFS: failed to read tree root on dm-2 Oct 27 12:30:46 linux.site kernel: parent transid verify failed on 1012842496 wanted 663592 found 663596 Oct 27 12:30:46 linux.site kernel: parent transid verify failed on 1012842496 wanted 663592 found 663596 Oct 27 12:30:46 linux.site kernel: BTRFS: failed to read tree root on dm-2 Oct 27 12:30:46 linux.site kernel: BTRFS: open_ctree failed linux:/home/linux # btrfs --version Btrfs v3.16.1+20140922