On 2018/10/10 下午12:47, Shapranov Vladimir wrote: > Hi, > > I've got a filesystem with first ~50Mb accidentally dd'ed.
So about 49M meta/data loss. It depends on the chunk layout. If it got one metadata chunk wiped out, it's pretty hard to repair. If it only wiped several data chunks, it should be mostly OK. > > "btrfs check" fails with a following error (regardless of "-s"): > checksum verify failed on 21037056 found FC8A6557 wanted 2F51D090 > checksum verify failed on 21037056 found FC8A6557 wanted 2F51D090 > checksum verify failed on 21037056 found 1EDD5E47 wanted 222F7E7F > checksum verify failed on 21037056 found 1EDD5E47 wanted 222F7E7F > bytenr mismatch, want=21037056, have=13515002166904211737 > ERROR: cannot read chunk root > ERROR: cannot open file system > > "mount -o ro /dev/sdf1 /mnt/tmp" fails, while "mount -o ro,subvol=X /mnt/tmp" > succeeds for "/" and couple subvolumes. That's very strange. If chunk root is corrupted, it should fail for all subvolumes. > > I can even ls the root directory, but at some point something can't be read > anymore and following errors appear in dmesg: > [385647.999981] btrfs_dev_stat_print_on_error: 158686 callbacks suppressed > [385648.079187] BTRFS error (device sdd1): bdev /dev/sdf1 errs: wr 0, rd > 22094847, flush 0, corrupt 0, gen 0 > [385648.193733] BTRFS error (device sdd1): bdev /dev/sdf1 errs: wr 0, rd > 22094848, flush 0, corrupt 0, gen 0 > > Also it is worth mentioning that after corruption one of the subvolumes was > mounted read-write and possibly some files were written. > > Is there any chance to recover the FS? You could try btrfs rescue chunk-recovery to recover the chunk root, and then all depends on your luck to see if it works. Thanks, Qu > > >
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