[Xen-users] Severe slow disk write issue on LVM-deployed DomU

[g <g.d.monnezza@xxxxxxxxxx>]

Hi everyone.
I have a really severe performance issue on disk write on my domU's PV guest.
- Xen 4.1 fresh install on Debian Wheezy (kernel 3.2.0-4-amd64) via apt-get
- Simple disk (no raid) for Linux/Xen Dom0 installation
- LVM2 on top of raid5 disk raid5 disk for storing DomU
- Single LV for each DomU

The problem
While write speed (mesured via dd command) on Dom0 is near 163MB/s on the mounted DomU LV , the same dd command provides 8MB/s if executed within
the running DomU (with "noop" I/O scheduler set)
Running "top" in DomU, i  get high load average due to high %wa (no high CPU load)

DomU disk is submitted to Xen via configuration file with:
disk  = [ 'phy:/dev/xenstore/test,xvda1,w' ]

If the same DomU is deployed on file image ("test.img" cloned from "test" LV), write speed rise up to 63MB/s
disk  = [ 'file:/home/test.img,xvda1,w' ]

Obviously I can provide further detailed configuration parameters

Does anyone faced to the same problem? Does anyone can point me in the right direction?

I'm loosing my nights trying to solve this issue :( , please help!!

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