Hi Wenruo,
> On 2018年01月22日 09:11, Qu Wenruo wrote:
> >
> >
> > 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
backup_tree_root: 26008360648704 gen: 318590 level: 1
backup_tree_root: 26008365793280 gen: 318591 level: 1
backup_tree_root: 26008367398912 gen: 318592 level: 1
backup_tree_root: 26008375640064 gen: 318593 level: 1
> >
> > And try them one by one:
> >
> > # btrfs check --tree-root <number from above output> <device>
Seems like they're all part of the drive's bad sectors:
# btrfs check --tree-root 26008360648704 /dev/datavol/edata
bytenr mismatch, want=26008360648704, have=0
Couldn't read tree root
ERROR: cannot open file system
# btrfs check --tree-root 26008365793280 /dev/datavol/edata
bytenr mismatch, want=26008365793280, have=0
Couldn't read tree root
ERROR: cannot open file system
# btrfs check --tree-root 26008367398912 /dev/datavol/edata
bytenr mismatch, want=26008367398912, have=0
Couldn't read tree root
ERROR: cannot open file system
# btrfs check --tree-root 26008375640064 /dev/datavol/edata
bytenr mismatch, want=26008375640064, have=0
Couldn't read tree root
ERROR: cannot open file system
>
> And find-root output can also be tried here.
>
> But please keep in mind, the older generation is, the less chance.
After the first 10 or so entries from btrfs-find-root, btrfs check
wouldn't even recognise the root nodes. So it seems like this is a
gone case?
>
> Thanks,
> Qu
>
> >
> > 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
> >> --
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> >>
> >
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