Re: btrfs check --repair: ERROR: cannot read chunk root

[Marc MERLIN <marc@merlins.org>]

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On Mon, Oct 31, 2016 at 08:44:12AM +0000, Hugo Mills wrote:
> > Any idea on special dm setup which can make us fail to read out some
> > data range?
> 
>    I've seen both btrfs check and btrfs dump-super give wrong answers
> (particularly, some addresses end up larger than the device, for some
> reason) when run on a mounted filesystem. Worth ruling that one out.

I just finished running my scrub overnight, and it failed around 10%:
[115500.316921] BTRFS error (device dm-0): bad tree block start 8461247125784585065 17619396231168
[115500.332354] BTRFS error (device dm-0): bad tree block start 8461247125784585065 17619396231168
[115500.332626] BTRFS: error (device dm-0) in __btrfs_free_extent:6954: errno=-5 IO failure
[115500.332629] BTRFS info (device dm-0): forced readonly
[115500.332632] BTRFS: error (device dm-0) in btrfs_run_delayed_refs:2960: errno=-5 IO failure
[115500.436002] btrfs_printk: 550 callbacks suppressed
[115500.436024] BTRFS warning (device dm-0): Skipping commit of aborted transaction.
[115500.436029] BTRFS: error (device dm-0) in cleanup_transaction:1854: errno=-5 IO failure


myth:~# ionice -c 3 nice -10 btrfs scrub start -Bd /mnt/mnt
(...)
scrub device /dev/mapper/crypt_bcache0 (id 1) canceled
        scrub started at Sun Oct 30 22:52:59 2016 and was aborted after 09:03:11
        total bytes scrubbed: 1.15TiB with 512 errors
        error details: csum=512
        corrected errors: 0, uncorrectable errors: 512, unverified errors: 0

Am I correct that if I see "__btrfs_free_extent:6954: errno=-5 IO failure" it means
that btrfs had physical read errors from the underlying block layer?

Do I have some weird mismatch between the size of my md array and the size of my filesystem
(as per dd apparently thinking parts of it are out of bounds?)
Yet,  the sizes seem to match:


myth:~#  mdadm --query --detail /dev/md5
/dev/md5:
        Version : 1.2
  Creation Time : Tue Jan 21 10:35:52 2014
     Raid Level : raid5
     Array Size : 15627542528 (14903.59 GiB 16002.60 GB)
  Used Dev Size : 3906885632 (3725.90 GiB 4000.65 GB)
   Raid Devices : 5
  Total Devices : 5
    Persistence : Superblock is persistent

  Intent Bitmap : Internal

    Update Time : Mon Oct 31 07:56:07 2016
          State : clean 
 Active Devices : 5
Working Devices : 5
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 512K

           Name : gargamel.svh.merlins.org:5
           UUID : ec672af7:a66d9557:2f00d76c:38c9f705
         Events : 147992

    Number   Major   Minor   RaidDevice State
       0       8       97        0      active sync   /dev/sdg1
       6       8      113        1      active sync   /dev/sdh1
       2       8       81        2      active sync   /dev/sdf1
       3       8       65        3      active sync   /dev/sde1
       5       8       49        4      active sync   /dev/sdd1

myth:~# btrfs fi df /mnt/mnt
Data, single: total=13.22TiB, used=13.19TiB
System, DUP: total=32.00MiB, used=1.42MiB
Metadata, DUP: total=75.00GiB, used=72.82GiB
GlobalReserve, single: total=512.00MiB, used=6.73MiB

Thanks,
Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/  

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