Re: Random data corruption in VM, possibly caused by rbd

[Guido Winkelmann <guido-ceph@thisisnotatest.de>]

Am Montag, 11. Juni 2012, 09:30:42 schrieb Sage Weil:
> On Mon, 11 Jun 2012, Guido Winkelmann wrote:
> > Am Freitag, 8. Juni 2012, 06:55:19 schrieb Sage Weil:
> > > On Fri, 8 Jun 2012, Oliver Francke wrote:

> > > Are you guys able to reproduce the corruption with 'debug osd = 20' and
> > > 
> > > 'debug ms = 1'?  Ideally we'd like to:
> > >  - reproduce from a fresh vm, with osd logs
> > >  - identify the bad file
> > >  - map that file to a block offset (see
> > >  
> > >    http://ceph.com/qa/fiemap.[ch], linux_fiemap.h)
> > >  
> > >  - use that to identify the badness in the log
> > > 
> > > I suspect the cache is just masking the problem because it submits fewer
> > > IOs...
> > 
> > Okay, I added 'debug osd = 20' and 'debug ms = 1' under [global] and
> > 'filestore fiemap = false' under [osd] and started a new VM. That worked
> > nicely, and the iotester found no corruptions. Then I removed 'filestore
> > fiemap = false' from the config, restarted all osds and ran the iotester
> > again. Output is as follows:
> > 
> > testserver-rbd11 iotester # date ; ./iotester /var/iotest ; date
> > Mon Jun 11 17:34:44 CEST 2012
> > Wrote 100 MiB of data in 1943 milliseconds
> > Wrote 100 MiB of data in 1858 milliseconds
> > Wrote 100 MiB of data in 2213 milliseconds
> > Wrote 100 MiB of data in 3441 milliseconds
> > Wrote 100 MiB of data in 2705 milliseconds
> > Wrote 100 MiB of data in 1778 milliseconds
> > Wrote 100 MiB of data in 1974 milliseconds
> > Wrote 100 MiB of data in 2780 milliseconds
> > Wrote 100 MiB of data in 1961 milliseconds
> > Wrote 100 MiB of data in 2366 milliseconds
> > Wrote 100 MiB of data in 1886 milliseconds
> > Wrote 100 MiB of data in 3589 milliseconds
> > Wrote 100 MiB of data in 1973 milliseconds
> > Wrote 100 MiB of data in 2506 milliseconds
> > Wrote 100 MiB of data in 1937 milliseconds
> > Wrote 100 MiB of data in 3404 milliseconds
> > Wrote 100 MiB of data in 1990 milliseconds
> > Wrote 100 MiB of data in 3713 milliseconds
> > Read 100 MiB of data in 4856 milliseconds
> > Digest wrong for file
> > "/var/iotest/b45e1a59f26830fb98af1ba9ed1360106f5580aa" Mon Jun 11
> > 17:35:34 CEST 2012
> > testserver-rbd11 iotester # ~/fiemap
> > /var/iotest/b45e1a59f26830fb98af1ba9ed1360106f5580aa
> > File /var/iotest/b45e1a59f26830fb98af1ba9ed1360106f5580aa has 1 extents:
> > #       Logical          Physical         Length           Flags
> > 0:      0000000000000000 00000000a8200000 0000000000100000 000
> > 
> > I looked into the file in question, and it started with zero-bytes from
> > the
> > start until position 0xbff, even though it was supposed to all random
> > data.
> > 
> > I have included timestamps in the hopes they might make it easier to find
> > the related entries in the logs.
> > 
> > So what do I do now? The logs are very large and complex, and I don't
> > understand most of what's in there. I don't even know which OSD served
> > that
> > particular block/object.
> 
> If you can reproduce it with 'debug filestore = 20' too, that will be
> better, as it will tell us what the FIEMAP ioctl is returning.  Also, if
> you can attach/post the contents of the object itself (rados -p rbd get
> rb.0.1.0000000002a0 /tmp/foo) we can make sure the object has the right
> data (and the sparse-read operation that librbd is doing is the culprit).

Um. Maybe... That's the problem with using random data, I can't just look at 
it and recognize it. I guess tomorrow I'll slap something together to see if I 
can find any 1 Meg-range of data in there that matches the expect checksum.

> 
> As for the log:
> 
> First, map the offset to an rbd block.  For example, taking the 'Physical'
> value of 00000000a8200000 from above:
> 
> $ printf "%012x\n" $((0x00000000a8200000 / (4096*1024) ))
> 0000000002a0
> 
> Then figure out what the object name prefix is:
> 
> $ rbd info <imagename> | grep prefix
>         block_name_prefix: rb.0.1
> 
> Then add the block number, 0000000002a0 to that, e.g. rb.0.1.0000000002a0.
> 
> Then map that back to an osd with
> 
> $ ceph osd map rbd rb.0.1.0000000002a0
> osdmap e19 pool 'rbd' (2) object 'rb.0.1.0000000002a0' -> pg 2.a2e06f65
> (2.5) -> up [0,2] acting [0,2]
> 
> You'll see the osd ids listed in brackets after 'active'.  We want the
> first one, 0 in my example.  The log from that OSD is what we need.

I'm getting

osdmap e89 pool 'rbd' (2) object 'rb.0.13.0000000002a0' -> pg 2.aca5eccb 
(2.4b) -> up [1,2] acting [1,2]

from that command, so I guess it's osd.1 then.
Do you have somewhere I can upload the log? It is 1.1 GiB in size. Bzip2 gets 
it down to 53 MiB, but that's still too large to be sent to a mailing list...

	Guido