Re: all rbd users: set 'filestore fiemap = false'

[Oliver Francke <Oliver.Francke@filoo.de>]

Hi Sage,

On 06/18/2012 06:02 AM, Sage Weil wrote:
> If you are using RBD, and want to avoid potential image corruption, add
>
> 	filestore fiemap = false
>
> to the [osd] section of your ceph.conf and restart your OSDs.

as far as this heals some trouble, but I fairly don't understand...

>
> We've tracked down the source of some corruption to racy/buggy FIEMAP
> ioctl behavior.  The RBD client (when caching is diabled--the default)
> uses a 'sparse read' operation that the OSD implements by doing an fsync
> on the object file, mapping which extents are allocated, and sending only
> that data over the wire.  We have observed incorrect/changing FIEMAP on
> both btrfs:
>
> 	fsync
> 	fiemap returns mapping
> 	<time passes, no modifications to file>
> 	fiemap returns different mapping

... that even an initial start of a VM leads to corruption of the read data?

I get s/t like:

--- 8-< ---

Loading, please wait
/sbin/init: relocation error: ...
  not defined in file libc.so.6...
[     0.81...] Kernel panic - not snycing: Attempted to kill init!

--- 8-< ---

host-kernel is now 3.4.1 + qemu-1.0.1, but shows failures with other 
kernel/qemu-versions, too.

Keeping fingers crossed for Josh, though ;-)
Give me a shout, If I can do some debugging,

regards,

Oliver.

>
> Josh is still tracking down which kernels and file system are affected;
> fortunately it is relatively easy to reproduce with the test_librbd_fsx
> tool.  In the meantime, the (mis)feature can be safely disabled. It will
> default to off in 0.48. It is unclear whether it's really much of a
> performance win anyway.
>
> Thanks!
> sage
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Oliver Francke

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