multiple writes of same block

[Eyal Lebedinsky <eyal@eyal.emu.id.au>]

Using XFS (latest 2.4.9-xfs) over raid5 I got a message:
	raid5: multiple 1 requests for sector 24663824
and the explanation I got from the raid list is:

> It means that while raid5 had an outstanding write request on a
> particular sector, it received another write request for the same
> sector.
> 
> It trys to do the right thing and write them both out in the order
> that it received them, but it is a bit of a worry that any filesystem
> would do this.  I'm guessing that Andrew is using XFS too.  Is that
> right?
> 
> While raid5 tries to keep the requests in order, and I suspect other
> drivers do to, I don't think that it is reasonable to assume that no
> device driver will ever re-order two requests for the same sector.
> If I were the author of the filesystem I would be worried.
> 
> NeilBrown

This truely sounds worrying. Is this OK to be this way or is this
an issue that needs fixing?

--
Eyal Lebedinsky (eyal@eyal.emu.id.au) <http://samba.anu.edu.au/eyal/>