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Re: [Xen-devel] why do I get bad disk write performance in the kernel 3.

On Thu, 2011-11-10 at 14:25 +0000, Roberto Scudeller wrote:
> Ian,
>         That depends on whether Roberto is using xm/xend or xl, I
>         think.
>         Roberto?
> I'm using "xl create windows.cfg"

OK, so you will be getting qdisk (and your logs confirm this).
>         > You could also try the 'file:/local-disk' which will setup a
>         loopback device
>         > and use that. Try that as well.
>         This is true with xm/xend but with xl you will need to
>         manually setup
>         the looback and use phy:/dev/loop in order to perform this
>         experiment.
>         For xl file: turns into qdisk unless blktap is available.
> I'm execute with file:/, but in xenstore-list, continue with qdisk.

Please try using losetup to bind your file to /dev/loopN and specifying
phy:/dev/loopN in your config. That should get you blkback.

> I try with "file://" and result was qdisk again. Do you think is LVM
> test need?

That would also be interesting.

> Why did kernel 3.1 use the qdisk? I want to use blktap backend
> ('tap2:aio:/disk-local/xvda,xvda,w').

blktap is not available in 3.1. Unfortunately it is not upstreamable so
it is unlikely to become available until someone does a pile of work to
make it a userspace only thing (see the list archives for various
explanations of this).

Since you are using a raw image (rather than e.g. vhd or qcow) there is
no benefit to blktap.


> Thanks for help.
> -- 
> Roberto Scudeller

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