March 03, 2010, 8:39 PM — Last week, Microsoft released a set of drivers that allow production versions of Red Hat to run on Hyper-V. The drivers, otherwise known as integration components, have some limitations, but they come with the full assurance that both Microsoft and Red Hat will support such an implementation.
Specifically the drivers support RHEL 5.2, 5.3, and 5.4. These drivers also support SUSE Linux Enterprise Server 10 SP2 x86 and x64, and SUSE Linux Enterprise Server 11 x86 and x64, but that's old news.
With much fanfare, Microsoft first submitted said drivers to the Linux kernel way back in July (its first, and so far only, contribution to Linux, for obvious reason). Those drivers were already tested to work with Red Hat and, of course, SUSE. And in October, Red Hat and Microsoft announced that they were joining each other's virtualization partnership programs, and validated that their products worked on each other's virtual machines. So what took Microsoft so long to release these Red Hat drivers to the public?
That's one of the questions I put to Microsoft's Vijay Tewari, principal program manager with the Windows Virtualization Team. In short, the delay was caused by one issue: the two companies hadn't worked out a deal on who would support the Red Hat operating system if it was running as a Hyper-V guest. The support issue was solved a couple of weeks ago (and I'm getting to the details on that in a minute) and hence the drivers were made public. (Download them here.)
Limited to one virtual processor
First, let's note the limitations. Red Hat virtual machines running on Hyper-V are limited to a single virtual processor, which limits the size of the Linux workload. But Tewari says that this limitation isn't specific to just Red Hat. SUSE is also limited to one VP. The number of VPs varies for different versions of Windows Server, too. WS 2008 R2 VMs have access to four VPs, WS3003 gets 3. Tewari says that Microsoft is working on increasing the number of VPs for Linux servers on Hyper-V.
Limited Mouse support
Second, the components themselves don't provide mouse support, although Citrix makes an add-on, Project Satori, that fixes this issue. The mouse works if you are physically accessing the server. But, without the add-in, isn't available if you RDP into the machine and launch the console of the guest operating system via your remote connection, says Tewari.
Hyper-V Linux driver code has forked
These drivers began life as the same ones submitted to the Linux Kernel in July, 2009, but, as those originals have been modified with patches and changes from the Linux community, the code bases between this download and the Linux kernel have forked. Microsoft says that over the next few months, it will integrate them back into a single code base. But, says Tewari, the fork was inevitable because the Hyper-V drivers were submitted to the latest stable version of the kernel at the time, 2.6.32 (version 2.6.33 became available late last month). Not all the commercial distributions are using that release. These drivers support Red Hat based on 2.6.18 and 2.6.27, for instance.
As part of the work of reuniting the code again, Microsoft promises to include some enhancements, such as a fix for the mouse issue.
How Red Hat will support
Red Hat has promised that the Hyper-V drivers will eventually become a native part of its distribution. That will in all likelihood occur whenever Red Hat upgrades its commercial product to kernel 2.6.32 or later. Indeed, this is the reason why Microsoft swallowed crow and submitted its drivers to the kernel in the first place, under the GPL no less. This even though it continues to toy with the threat that Linux violates its patents. (Last week, Microsoft made two announcements that harked back to its threats: One with Amazon and another with Panasonic ... but I digress.)
