Re: Problem with inconsistent PG

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Hi Sage, *,

your tip with truncating from below did not solve the problem. Just to recap:

we had two inconsistencies, which we could break down to something like:

rb.0.0.000000000000__head_DA680EE2

according to the ceph dump from below. Walking to the node with the OSD mounted on /data/osd3
for example, and a stupid "find …" brings up a couple of them, so the pg number is relevant too -
makes sense - we went into lets say "/data/osd3/current/84.2_head/" and did a hex dump from the file, looked really
like the "head", in means of signs from an installed grub-loader. But a corrupted partition-table.
>From other of these files one could do a "fdisk -l <file>" and at least a partition-table could have been
found.
Two days later we got a customers big complaint about not being able to boot his VM anymore. The point now is,
from such a file with name and pg, how can we identify the real file being associated with, cause there is another
customer with a potential problem with next reboot ( second inconsistency).

We also had some VM's in a big test-phase with similar problems… grub going into rescue-prompt, invalid/corrupted
partition tables, so all in the first "head-file"?
Would be cool to get some more infos… and sched some light into the structures ( myself not really being a good code-reader
anymore ;) ).

Thanks in@vance and kind regards,

Oliver.

Am 13.02.2012 um 18:13 schrieb Sage Weil:

> On Sun, 12 Feb 2012, Jens Rehpoehler wrote:
> 
>>>> Hi Liste,
>>>> 
>>>> today i've got another problem.
>>>> 
>>>> ceph -w shows up with an inconsistent PG over night:
>>>> 
>>>> 2012-02-10 08:38:48.701775    pg v441251: 1982 pgs: 1981 active+clean, 1
>>>> active+clean+inconsistent; 1790 GB data, 3368 GB used, 18977 GB / 22345
>>>> GB avail
>>>> 2012-02-10 08:38:49.702789    pg v441252: 1982 pgs: 1981 active+clean, 1
>>>> active+clean+inconsistent; 1790 GB data, 3368 GB used, 18977 GB / 22345
>>>> GB avail
>>>> 
>>>> I've identified it with "ceph pg dump - | grep inconsistent
>>>> 
>>>> 109.6    141    0    0    0    463820288    111780    111780
>>>> active+clean+inconsistent    485'7115    480'7301    [3
>>>> <http://marc.info/?l=ceph-devel&m=132891306919981&w=2#3>,4
>>>> <http://marc.info/?l=ceph-devel&m=132891306919981&w=2#4>]    [3
>>>> <http://marc.info/?l=ceph-devel&m=132891306919981&w=2#3>,4
>>>> <http://marc.info/?l=ceph-devel&m=132891306919981&w=2#4>]
>>>> 485'7061    2012-02-10 08:02:12.043986
>>>> 
>>>> Now I've tried to repair it with: ceph pg repair 109.6
>>>> 
>>>> 2012-02-10 08:35:52.276325 mon<- [pg,repair,109.6]
>>>> 2012-02-10 08:35:52.276776 mon.1 ->  'instructing pg 109.6 on osd.3 to
>>>> repair' (0)
>>>> 
>>>> but i only get the following result:
>>>> 
>>>> 2012-02-10 08:36:18.447553   log 2012-02-10 08:36:08.455420 osd.3
>>>> 10.10.10.8:6801/25980 6913 : [ERR] 109.6 osd.4: soid
>>>> 1ef398ce/rb.0.0.0000000000bd/headsize 2736128 != known size 3145728
>>>> 2012-02-10 08:36:18.447553   log 2012-02-10 08:36:08.455426 osd.3
>>>> 10.10.10.8:6801/25980 6914 : [ERR] 109.6 scrub 0 missing, 1 inconsistent
>>>> objects
>>>> 2012-02-10 08:36:18.447553   log 2012-02-10 08:36:08.455799 osd.3
>>>> 10.10.10.8:6801/25980 6915 : [ERR] 109.6 scrub 1 errors
>>>> 
>>>> Can someone please explain me what to do in this case and how to recover
>>>> the pg ?
>>> 
>>> So the "fix" is just to truncate the file to the expected size, 3145728,
>>> by finding it in the current/ directory.  The name/path will be slightly
>>> weird; look for 'rb.0.0.0000000000bd'.
>>> 
>>> The data is still suspect, though.  Did the ceph-osd restart or crash
>>> recently?  I would do that, repair (it should succeed), and then fsck the
>>> file system in that rbd image.
>>> 
>>> We just fixed a bug that was causing transactions to leak across
>>> checkpoint/snapshot boundaries.  That could be responsible for causing all
>>> sorts of subtle corruptions, including this one.  It'll be included in
>>> v0.42 (out next week).
>>> 
>>> sage
>> 
>> Hi Sarge,
>> 
>> no ... the osd didn't crash. I had to do some hardware maintainance and push
>> it
>> out of distribution with "ceph osd out 3". After a short while i used
>> "/etc/init.d/ceph stop" on that osd.
>> Then, after my work i've started ceph and push it in the distribution with
>> "ceph osd in 3".
> 
> For the bug I'm worried about, stopping the daemon and crashing are 
> equivalent.  In both cases, a transaction may have been only partially 
> included in the checkpoint.
> 
>> Could you please tell me if this is the right way to get an osd out for
>> maintainance ? Is there
>> any other thing i should do to keep data consistent ?
> 
> You followed the right procedure.  There is (hopefully, was!) just a bug.
> 
> sage
> 
> 
>> My structure is ->  3 MDS/MON Server on seperate Hardware Nodes an 3 OSD Nodes
>> with a each a total capacity
>> of 8 TB. Journaling is done on a separate SSD per node. The whole thing is a
>> data store for a kvm virtualisation
>> farm. The farm is accessing the data directly per rbd.
>> 
>> Thank you
>> 
>> Jens
>> 
>> 
>> 
>> 
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