Re: Input/output error on newly created file

[Nikolaus Rath <Nikolaus@rath.org>]

On May 09 2016, Filipe Manana <fdmanana@gmail.com> wrote:
> On Sun, May 8, 2016 at 11:18 PM, Nikolaus Rath <Nikolaus@rath.org> wrote:
>> Hello,
>>
>> I just created an innocent 10 MB on a btrfs file system, yet my attempt
>> to read it a few seconds later (and ever since), just gives:
>>
>> $ ls -l in-progress/mysterious-io-error
>> -rw-rw-r-- 1 nikratio nikratio 10485760 May  8 14:41 in-progress/mysterious-io-error
>> $ cat in-progress/mysterious-io-error
>> cat: in-progress/mysterious-io-error: Input/output error
>
> If you unmount and mount again the filesystem, does it happen again?

After rebooting, the previously unaccessible file can now be read. But I
cannot tell if it contains the right data.

However, I just encountered the same problem with another, freshly
created file.

> How did you create the file?

In Python 3. The equivalent code is more or less:

with open('file.dat', 'wb+') as fh:
     for buf in generate_data():
         fh.write(buf) # bufsize is about 128 kB


However, I should note that there is a lot of activity in this
file system (it contains my home directory), so the above alone will
probably not reproduce the problem.

That said, so far both the problematic files were created by the same
application (S3QL, of which luckily I am also the maintainer).


> Does fsck reports any issues?

Do you mean btrfsck? It actually has a lot to say:

checking extents
checking free space cache
checking fs roots
root 5 inode 3149867 errors 400, nbytes wrong
root 5 inode 3150237 errors 400, nbytes wrong
root 5 inode 3150238 errors 400, nbytes wrong
root 5 inode 3150242 errors 400, nbytes wrong
root 5 inode 3150260 errors 400, nbytes wrong
[...]
root 5 inode 15595011 errors 400, nbytes wrong
root 5 inode 15595016 errors 400, nbytes wrong
Checking filesystem on /dev/mapper/vg0-nikratio_crypt
UUID: 8742472d-a9b0-4ab6-b67a-5d21f14f7a38
found 263648960636 bytes used err is 1
total csum bytes: 395314372
total tree bytes: 908644352
total fs tree bytes: 352735232
total extent tree bytes: 95039488
btree space waste bytes: 156301160
file data blocks allocated: 675209801728
 referenced 410351722496
Btrfs v3.17

However, the inode of the problematic file (16186241) is not
mentioned. But I guess this is not surprising, because also for this
file, I can read the contents after remounting.


Best,
-Nikolaus


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