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[Xen-devel] Hacking XenEnterprise / Please Help
My company would very much like to use Xen for the big virtualization
pipeline that were putting together, but we seem to be starved for
We need the following features in Xen and we're trying to figure out
the best way to acquire them.
1. Full virtualization of Windows XP
2. Shared Windows boot image with copy-on-write backing storage after
3. Ability to shut down a Windows VM and examine the copy-on-write
file store for data written to the drive.
4. High-performance hyper-virtualized Windows drivers
The most direct solutions to this problem seems to be:
1. XenEnterprise with it's hyper-virtualized Windows drivers and
using QCOW files for copy-on-write file store.
Except my experimentation with 3.1.0 last week showed me that there's
a bug that prevents blk:tap I/O (which qcow uses) from working
correctly with fully virtualized domains. I did see the patch and
would be willing to use it against the 3.1.0 source tree except that
I don't know if I can even make that drastic of a modification to a
The other XenEnterprise possibility is to bypass blk:tap and simply
use LVM snapshots as copy-on-write images. This works on RHEL 5, but
XenEnterprise didn't have a required kernel feature enabled to allow
it. That means I would need to modify the XenEnterprise kernel to
enable the feature or go back and hack the version of Xen to allow
In either case, it's a significant modification of a turnkey package.
2. RHEL 5/Centos 5 with the updated XenSource 3.1.0 RPMs.
I had this running pretty well. The device mapper in the XenSource
3.1.0 kernel for RHEL 5 allowed LVM snapshot copy-on-writes and I
could probably use the blk:tap patch if I didn't mind recompiling the
Unfortunately we can't use the hypervirtualized windows drivers
unless we're running XenEnterprise.
So.... we're between a rock and a hard place. We need high-
performance copy-on-write Windows virtualization. XenSource makes
it impossible to use the hypervirtualized windows drivers in anything
but XenEnterprise, but they restrict the XenEnterprise kernel to the
feature set that they deem necessary and which falls short of our needs.
I wouldn't mind modifying XenEnterprise in some way, but I fear that
the XenEnterprise kernel modifications are closed, or our changes
wouldn't be supported.
If an *Engineer at XenSource* could refer this to the correct sales/
pre-sales engineering people I would greatly appreciate it --- we're
running out of time and this could be a huge and high-profile Xen
installation. I've already contacted front-line sales in
California and they seem to want to hand us off to third-party
Perhaps we could license the windows drivers for use under RHEL/Centos?
We have no one to contact other than engineers we've chatted with at
XenSource through this mailing list. Otherwise, discussing this
issue with front-line sales people is highly unproductive.
*HINT* This is your chance to win business from VMWare.
Any help greatly appreciated...
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