[ 1821.067656] BTRFS: device fsid 240e9ce6-df7d-4318-bdb3-52411817a94d devid 1 transid 3167 /dev/dm-14 scanned by systemd-udevd (15391)
[ 1845.780336] BTRFS info (device dm-14): using crc32c (crc32c-intel) checksum algorithm
[ 1845.780361] BTRFS info (device dm-14): using free space tree
[ 1845.791949] BTRFS error (device dm-14): parent transid verify failed on logical 305749557248 mirror 1 wanted 3155 found 3975
[ 1845.791967] BTRFS error (device dm-14): failed to read block groups: -5
[ 1845.793087] BTRFS error (device dm-14): open_ctree failed

root@sandisk2: /media/sda1 # btrfsck /dev/san/root 
Opening filesystem to check...
parent transid verify failed on 305749557248 wanted 3155 found 3975
parent transid verify failed on 305749557248 wanted 3155 found 3975
Ignoring transid failure
ERROR: child eb corrupted: parent bytenr=6782976 item=177 parent level=1 child bytenr=305749557248 child level=2
ERROR: failed to read block groups: Input/output error
ERROR: cannot open file system

root@archlinux: /media # btrfs check --repair /dev/san/root 
enabling repair mode
WARNING:

        Do not use --repair unless you are advised to do so by a developer
        or an experienced user, and then only after having accepted that no
        fsck can successfully repair all types of filesystem corruption. Eg.
        some software or hardware bugs can fatally damage a volume.
        The operation will start in 10 seconds.
        Use Ctrl-C to stop it.