今日から外付けハードドライブのbtrfsボリュームに適切な量のデータ（MBの範囲）を書き込もうとすると、ボリュームが読み取り専用に切り替わり、操作が中断されます。ボリュームは非常に簡単です（RAIDなし、スナップショットなし）。
journalctl書き込み中に次のように表示されます。
Jan 23 18:34:16 my-machine kernel: BTRFS: device label <...> devid 1 transid 3344 /dev/sdb1 Jan 23 18:34:16 my-machine kernel: BTRFS info (device sdb1): disk space caching is enabled Jan 23 18:34:16 my-machine kernel: BTRFS info (device sdb1): has skinny extents Jan 23 18:36:35 my-machine kernel: BTRFS critical (device sdb1): corrupt node: root=7 block=253655810048 slot=106, bad key order, current (18446744073709551606 128 9223372601711906816) next (18446744073709551606 128 564873670656) Jan 23 18:38:13 my-machine kernel: BTRFS critical (device sdb1): corrupt node: root=7 block=253655810048 slot=106, bad key order, current (18446744073709551606 128 9223372601711906816) next (18446744073709551606 128 564873670656) Jan 23 18:39:43 my-machine kernel: BTRFS critical (device sdb1): corrupt node: root=7 block=253655810048 slot=106, bad key order, current (18446744073709551606 128 9223372601711906816) next (18446744073709551606 128 564873670656) Jan 23 18:40:58 my-machine kernel: BTRFS critical (device sdb1): corrupt node: root=7 block=253655810048 slot=106, bad key order, current (18446744073709551606 128 9223372601711906816) next (18446744073709551606 128 564873670656) Jan 23 18:42:28 my-machine kernel: BTRFS critical (device sdb1): corrupt node: root=7 block=253655810048 slot=106, bad key order, current (18446744073709551606 128 9223372601711906816) next (18446744073709551606 128 564873670656) Jan 23 18:42:39 my-machine kernel: BTRFS critical (device sdb1): corrupt node: root=7 block=253655810048 slot=106, bad key order, current (18446744073709551606 128 9223372601711906816) next (18446744073709551606 128 564873670656) Jan 23 18:42:39 my-machine kernel: BTRFS critical (device sdb1): corrupt node: root=7 block=253655810048 slot=106, bad key order, current (18446744073709551606 128 9223372601711906816) next (18446744073709551606 128 564873670656) Jan 23 18:42:39 my-machine kernel: BTRFS: error (device sdb1) in btrfs_finish_ordered_io:3074: errno=-5 IO failure Jan 23 18:42:39 my-machine kernel: BTRFS info (device sdb1): forced readonly
最初は、btrfs check次の出力が提供されます。
$ sudo btrfsck /dev/sdb1 Checking filesystem on /dev/sdb1 UUID: a69162a3-aeb3-43c0-b74d-cfd280bfa8b6 checking extents bad block 253655810048 ERROR: errors found in extent allocation tree or chunk allocation checking free space cache checking fs roots checking csums there are no extents for csum range 563128786944-564280360960 csum exists for 563128786944-564280377344 but there is no extent record there are no extents for csum range 566428172288-567179472896 Right section didn't have a record there are no extents for csum range 565354430464-567179472896 Right section didn't have a record there are no extents for csum range 564280688640-567179472896 Right section didn't have a record there are no extents for csum range 564280639488-567179472896 csum exists for 564280639488-567179472896 but there is no extent record ERROR: errors found in csum tree found 1681395552256 bytes used, error(s) found total csum bytes: 0 total tree bytes: 2406924288 total fs tree bytes: 2279718912 total extent tree bytes: 123813888 btree space waste bytes: 350386565 file data blocks allocated: 1685019078656 referenced 1685018304512
を実行しましたが、btrfs scrub時にはそれ自体が動作を停止することがあります。その後、ドライブを再マウントする必要があります。
$ sudo btrfs scrub start -B /mnt/hd ERROR: scrubbing /mnt/hd failed for device id 1: ret=-1, errno=5 (Input/output error) scrub canceled for a69162a3-aeb3-43c0-b74d-cfd280bfa8b6 scrub started at Wed Jan 23 21:26:28 2019 and was aborted after 00:45:20 total bytes scrubbed: 509.99GiB with 0 errors
ただし、以下を使用してくださいbtrfs scrub resume。
$ sudo btrfs scrub status /mnt/hd scrub status for a69162a3-aeb3-43c0-b74d-cfd280bfa8b6 scrub resumed at Wed Jan 23 22:24:05 2019 and finished after 01:52:15 total bytes scrubbed: 1.20TiB with 27163 errors error details: csum=27163 corrected errors: 0, uncorrectable errors: 27163, unverified errors: 0
btrfs scrub私も実行する前に一度試してみましたbtrfs check --repair。以降の実行では、btrfs check「Bad Block 253655810048」の代わりに「Bad Block 253432905728」が表示されますが、これは大幅に変更されていないようです。今btrfs scrub終わったら、次のようにbtrfs check話してください。
Checking filesystem on /dev/sdb1 UUID: a69162a3-aeb3-43c0-b74d-cfd280bfa8b6 checking extents bad block 253432905728 ERROR: errors found in extent allocation tree or chunk allocation checking free space cache block group 253432430592 has wrong amount of free space, free space cache has 253722624 block group has 253689856 ERROR: free space cache has more free space than block group item, this could leads to serious corruption, please contact btrfs developers failed to load free space cache for block group 253432430592 ERROR: errors found in free space cache found 1681395535872 bytes used, error(s) found total csum bytes: 0 total tree bytes: 2406203392 total fs tree bytes: 2279718912 total extent tree bytes: 123797504 btree space waste bytes: 350047303 file data blocks allocated: 1685019078656 referenced 1685018304512
とても心配そうですね！どうやってこれが起こったのですか？ファイルシステムが本当に壊れているのでしょうか？それともドライブに問題がありますか（古いものでも全く使われず、SMARTに問題がないようです）