Well, turns out this was a more serious bug than we thought. With dm-thin overcommit, it causes this: [1324107.675334] BTRFS info (device dm-13): forced readonly [1324107.692909] BTRFS warning (device dm-13): Skipping commit of aborted transaction. [1324107.717141] BTRFS: error (device dm-13) in cleanup_transaction:1828: errno=-5 IO failure [1324107.743298] BTRFS info (device dm-13): delayed_refs has NO entry [1324107.817671] device-mapper: thin: 252:9: switching pool to write mode [1324108.662095] BTRFS error (device dm-13): bad tree block start, want 9050645626880 have 0 [1324108.694286] BTRFS error (device dm-13): bad tree block start, want 9050645626880 have 0 In other words, this broke my filesystem. I didn't try to see if it's damaged or just read-only, but obviously, this isn't good. New kernel should stop this from happening hopefully. VG/dm details if you care: VG Name vgds2 System ID Format lvm2 Metadata Areas 1 Metadata Sequence No 88 VG Access read/write VG Status resizable MAX LV 0 Cur LV 8 Open LV 7 Max PV 0 Cur PV 1 Act PV 1 VG Size 14.55 TiB PE Size 4.00 MiB Total PE 3815316 Alloc PE / Size 3801146 / 14.50 TiB Free PE / Size 14170 / 55.35 GiB VG UUID pc1cTH-kFo7-g0Kz-dELp-j51s-1yOO-v20WIV --- Logical volume --- LV Name thinpool2 VG Name vgds2 LV UUID rxJCsT-ImNv-ibvM-zOS0-Xzqv-O8AU-1STUH9 LV Write Access read/write LV Creation host, time gargamel.svh.merlins.org, 2018-07-26 08:42:51 -0700 LV Pool metadata thinpool2_tmeta LV Pool data thinpool2_tdata LV Status available # open 8 LV Size 14.50 TiB Allocated pool data 99.99% Allocated metadata 59.88% Current LE 3801088 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 8192 Block device 252:9 LV Path /dev/vgds2/ubuntu LV Name ubuntu VG Name vgds2 LV UUID y42AA8-5zfq-Vbmr-TNo9-g7rn-UbGf-KOnFrf LV Write Access read/write LV Creation host, time gargamel.svh.merlins.org, 2018-07-26 23:22:18 -0700 LV Pool name thinpool2 LV Status available # open 1 LV Size 14.00 TiB Mapped size 60.26% Current LE 3670016 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 8192 Block device 252:13 -- "A mouse is a device used to point at the xterm you want to type in" - A.S.R. Home page: http://marc.merlins.org/ | PGP 7F55D5F27AAF9D08
