[Xen-users] questions regarding HVM and maximum block device size

["Sebastian Reitenbach" <sebastia@xxxxxxxxxxxxxxxxxxxx>]

Hello list,

right now I run a bunch of PVM Xen guests, everything is fine. But on the 
horizon, there a potential need shows up, that I may have to run one or more 
HVM guests.

Some time ago, I did some tests, and I observed the following on a host:
I activated the AMD VT extension in the BIOS, because I wanted to test to 
setup a HVM machine. While this was activated, the PVM domU running on the 
same host, had a unusual slow NFS performance. After I was ready with the 
tests, I disabled the AMD VT in the BIOS again, and the NFS speed 
was "normal" again. The NFS speed with VT enabled was about 1/3rd slower 
than without. The dom0 and domU are 64Bit, SLES10SP1 systems.
Is this normal what I've seen? If yes, I guess it's not recommended to run 
PVM and HVM systems on the same dom0? Or if no, any idea, what I can do 
about it?

Further I'd like to know, whether a xm mem-set will work for HVM domU's?
I guess, in case the OS supports it, then it will work?
I've also read about paravirtual drivers for HVM guests, and I've seen a 
xen-balloon.ko for HVM Linux guests, but I want to run MS Windows, are there 
also such drivers available?

VMWare had, or still has, don't use it anymore since there is xen ;), a 
limit on the maximum size of a block device, at 2TB. So if I wanted to share 
a disk larger than 2TB, then the VMWare guest was/is only able to see the 
2TB but not more. Does in Xen exists a similar limit on block device size?

kind regards
Sebastian


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