Xen-like state :: Mike Neir's Page

Eeek. Yet again I have gone too long without posting. I'm thinking of starting a new category of posts for the entries that start off by saying "yah, I haven't posted in a long time." There have been so many of them as of late that I really should do it.

The holidays were both happy and tiresome, as per usual. I had all kinds of difficulty getting presents for everyone. I struck out the first four times I went shopping, and I was pretty distraught. I was successful eventually, and Christmas turned out well. I got some good gifts, and everyone seemed to enjoy the gifts I got for them.

It feels strange to enter another new year. It feels like I just moved in here, yet, I've been here an entire year. I just finished my fourth year at Liquid Web in December, yet I can still remember the old days at Jet Drive as if they were yesterday. My ten-year high school reunion takes place this year. When did I get old? I think I missed it.

Inspired by some happenings at work, I've been playing with Xen a fair amount over the past few weeks. Xen is a virualization system that allows for one to run multiple operating systems on the same computer simultaneously. WIth hardware that supports it, the virtualization can be done at a hardware level, allowing for unmodified guest operating systems to be run (including Windows). Otherwise, modifications must be made to the kernel to all guests for Xen to function properly. This limits the guest operating systems to open source OSs, which doesn't bother me much since linux is my OS of choice. I've placed Xen on my server at work, and I'm going to use it to set up seperate OS environments for seperate services that don't need to access the same data on the server. While it will introduce a bit of overhead, it will allow for a more secure system overall. If one environment is somehow compromised, the intrusion will be limited to that environment only. All in all, it's a very neat system.

Steve J :: 01/05/2007, 8:02 pm :: Reply

Doesn't VMWare run on Linux?

Mike Neir :: 01/06/2007, 12:13 am :: Reply

Yep, but you need a whole OS for it to run on top of. All of the OSs on the box run on top of Xen, including the OS that controls the others (domain 0).

Steve J :: 01/06/2007, 11:08 pm :: Reply

EMC does something like that called Centera, but that's a whole hardware / software package

Joel :: 01/07/2007, 6:51 pm :: Reply

...allowing for unmodified guest operating systems to be run (including Windows). Otherwise, modifications must be made to the kernel to all for Xen to function properly. This limits the guest operating systems to open source OSs...

Come again? Guest or host?

Mike Neir :: 01/07/2007, 8:12 pm :: Reply

The appropriate hardware support allows for unmodified guest operating systems. Without that support, you need to modify the guests. There is no "host" operating system per se, but there is one that interacts with Xen to control the execution of the guests. It doesn't run underneath the guests, rather alongside of them, with elevated privileges that allows it to control the other guests. This is called domain0 in Xen terms, and must be a modified to support the low-level Xen interfaces.

Michael :: 01/08/2007, 1:09 am :: Reply

There's a pretty good article on different virtualization techniques at http://www.ibm.com/developerworks/linux/library/l-linuxvirt/?ca=dgr-lnxw01Virtual-Linux, it's probably nothing we didn't know already but it explains a lot for people new to the idea of running multiple OSes.

Mike Neir :: 01/08/2007, 2:28 am :: Reply

That's a really good writeup. With hardware support, Xen can achieve full virtualization, but without the proper hardware, it can only achieve paravirtualization.