Infrastructure Software

Just thought I would post up my experiences with PXE booting Windows vm guests with OVM.

The reasoning behind PXE booting guests is that we were interested to find a way to assign storage to OVM guests directly off a SAN cluster without having to go through an manually hack the vm.cfg files of all the guests (we are using physical backed SAN RAW LUNs). Using a bit of software called 'Flex' from Doubletake (which we used for PXE booting bare metal / workstations off the SAN) - we successfully managed to get OVM Windows 2003 & Windows 2008 / R2 guests booting directly off the SAN via OVM PXE. This was great, as the Doubletake Flex storage management console is very much drag and drop - so it's super easy to assign / re-assign storage to VMs. In previous editions of OVM we were not able to get the PXE to work at all - so getting this to work was quite an exciting moment!

However - our elation was very much short lived.

We were of course using the HV drivers - and the NIC driver for this is 100Mb and SLOW.

Now last time I checked this is actually the same situation you have with Microsoft HyperV. You can only PXE from the 'Legacy NIC driver' however you CAN add a 2nd NIC and run this with the accelerated driver. So for HyperV you can boot off the legacy NIC and then use a 2nd iSCSI NIC for your swap, Applications etc. Not particularly neat - but it works.

Back to OVM.

First off - after upgrading to the PV drivers - PXE no longer works. You get to the 'loading Windows' screen - which then gives you a nice BSOD after about 5 minutes after it fails to hook up to a NIC driver for the rest of the boot process. For some reason, the OVM Windows PV drivers seem to have been written in such a way that they are 'hidden' from Microsofts iSCSI bootstrap. Doubletake have a tool in which you can boot off a CD - and manually assign a bootable NIC to the OS, but when the PV driver is installed - the NIC is gone.

Realising that it was going to be impossible to boot off the PV NIC - the next attempt was to copy Microsoft and boot off the Legacy one, handing over to the PV one once the OS loads.

OVM unfortunately does not let you assign different drivers to different NICs in VM Manager. If you change to PV (netfront) driver, both NICs get changed.

You CAN go in and hack the vm.cfg to manually change your boot NIC to the HV driver, leaving the other - but again - when the OS loads, the HV NIC still wants to at least appear to Windows as a PV NIC.

So it's strange. Before you add the PV drivers - your HV NIC is a Realteck - and PXE bootable.

If you then install the PV driver, and then manually hack the NIC back to HV driver - the NIC remains on the same driver.

Anyway - I'm afraid - that's as far as we got.

It would be nice if Oracle could ask MS why the PV NIC driver does not register as being iSCSI bootable...

Or perhaps at least better HV support / drivers?

It's a shame because I know that it's possible to boot OEL Guests PXE with the PV drivers - however - you can't migrate to a system like this unless you can get all your servers over to it....

Jeff