On 2018年01月22日 03:16, Liwei wrote: > Hi list, > > ====TLDR==== > 1. Can I mount a filesystem using one of the roots found with btrfs-find-root? Depends on the tree. If it's root tree, it's possible. Otherwise those found trees don't help much. > 2. Can btrfs check just fix the damaged root without attempting any > other repairs? No. But under most case, it's not a single corrupted tree but normally multiple. > 3. If the above is not possible, how should I proceed given that I > seem to have lost both the main and backup roots? In theory, it's possible to use specified fs tree root to salvage a filesystem. But under most case, metadata is protected by safer profile. So it's not implemented in btrfs-progs. Your current best try would be manually scanning through all tree backups. Which need extra info. Please provide the following info: # btrfs inspect dump-super -FfA <device> | grep backup_tree_root | sort | uniq And try them one by one: # btrfs check --tree-root <number from above output> <device> If any one can proceed, then use it to repair: # btrfs check --tree-root <number> <device> And good luck. Thanks, Qu > > ====Background Information==== > I have a 2x10TB raid0 (20TB, raid0 provided by md) volume that (my > theory is) experienced a headcrash while updating the root tree, or > maybe while it was carrying out background defragmentation.> > This occurred while I was setting up redundancy by using LVM > mirroring, so in the logs you'll see some dm errors. Unfortunately the > lost data has not been mirrored yet (what are the chances, given that > the mirror was 97% complete when this happened). > > Running a scrub on the raid shows that I have 1000+ unreadable > sectors, amounting to about 800kB of data. So I've got spare drives > and imaged the offending drive. Currently ddrescue is still trying to > read those sectors, but it seems unlikely that they'll ever succeed. > > ====Problem==== > So with an imaged copy of the array, I tried remounting the > filesystem, but it refuses to mount even using 'usebackuproot': > > With usebackuproot: > [ 1610.788527] device-mapper: raid1: Mirror read failed. > [ 1610.788799] device-mapper: raid1: Mirror read failed. > [ 1610.788939] Buffer I/O error on dev dm-15, logical block > 5371800560, async page read > [ 1610.823141] BTRFS: device label edata devid 1 transid 318593 > /dev/mapper/datavol-edata > [ 1616.778563] BTRFS info (device dm-15): trying to use backup root at > mount time > [ 1616.778758] BTRFS info (device dm-15): disk space caching is enabled > [ 1617.961152] device-mapper: raid1: Mirror read failed. > [ 1618.238198] device-mapper: raid1: Mirror read failed. > [ 1618.238498] BTRFS warning (device dm-15): failed to read tree root > [ 1618.238700] device-mapper: raid1: Mirror read failed. > [ 1618.238878] device-mapper: raid1: Mirror read failed. > [ 1618.239050] BTRFS warning (device dm-15): failed to read tree root > [ 1618.239207] device-mapper: raid1: Mirror read failed. > [ 1618.239372] device-mapper: raid1: Mirror read failed. > [ 1618.239590] BTRFS warning (device dm-15): failed to read tree root > [ 1618.239775] device-mapper: raid1: Mirror read failed. > [ 1618.240055] device-mapper: raid1: Mirror read failed. > [ 1618.240298] BTRFS warning (device dm-15): failed to read tree root > [ 1618.240492] device-mapper: raid1: Mirror read failed. > [ 1618.240744] device-mapper: raid1: Mirror read failed. > [ 1618.240989] BTRFS warning (device dm-15): failed to read tree root > [ 1618.363234] BTRFS error (device dm-15): open_ctree failed > > Without usebackuproot: > [ 2149.015427] device-mapper: raid1: Mirror read failed. > [ 2149.015700] device-mapper: raid1: Mirror read failed. > [ 2149.015840] Buffer I/O error on dev dm-15, logical block > 5371800560, async page read > [ 2154.172102] BTRFS info (device dm-15): disk space caching is enabled > [ 2155.325134] device-mapper: raid1: Mirror read failed. > [ 2155.715439] device-mapper: raid1: Mirror read failed. > [ 2155.715795] BTRFS warning (device dm-15): failed to read tree root > [ 2155.851599] BTRFS error (device dm-15): open_ctree failed > > It appears that the damaged data has affected both the main and > backup roots. > > Next I ran btrfs-find-root, which gave me the following: > Superblock thinks the generation is 318593 > Superblock thinks the level is 1 > Well block 25826479144960(gen: 318346 level: 1) seems good, but > generation/level doesn't match, want gen: 318593 level: 1 > Well block 25826450505728(gen: 318345 level: 1) seems good, but > generation/level doesn't match, want gen: 318593 level: 1 > Well block 25826461237248(gen: 318344 level: 1) seems good, but > generation/level doesn't match, want gen: 318593 level: 1 > Well block 25826479669248(gen: 318342 level: 0) seems good, but > generation/level doesn't match, want gen: 318593 level: 1 > Well block 25826479603712(gen: 318342 level: 0) seems good, but > generation/level doesn't match, want gen: 318593 level: 1 > Well block 25826468495360(gen: 318342 level: 0) seems good, but > generation/level doesn't match, want gen: 318593 level: 1 > Well block 25826465923072(gen: 318342 level: 0) seems good, but > generation/level doesn't match, want gen: 318593 level: 1 > Well block 25826477654016(gen: 318341 level: 0) seems good, but > generation/level doesn't match, want gen: 318593 level: 1 > ...[truncated] > > I tried running btrfs check with the top 5 roots, but only the > first 3 seems to be usable. However, even with the first 3, btrfs > check gives me a lot of: > bytenr mismatch, want=26008292753408, have=0 > bytenr mismatch, want=26353175658496, have=0 > bytenr mismatch, want=26353188618240, have=0 > bytenr mismatch, want=26353513299968, have=0 > and thousands of extent errors, etc. I do see references to > directories within the filesystem though, so I'd think the tree root > is at least pretty good. > > Just to see if btrfs check can reach a usable state, I made a COW > snapshot of the imaged drive, and ran btrfs check --repair. However, > it eventually gives up, and seemed to have wrecked the FS. > > Is there a way to mount/repair the filesystem with the found root > instead? I'd like to copy the files off the image, but prefer not to > use btrfs restore. Can btrfs check just copy the alternative root and > not try to repair anything else? > > ====Misc info==== > # uname -a > Linux tvm 4.14.0-3-amd64 #1 SMP Debian 4.14.13-1 (2018-01-14) x86_64 GNU/Linux > # btrfs --version > btrfs-progs v4.13.3 > > Thanks for the help! > Liwei > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html >
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