Questions[virtualization](server)

I have yet to see a system whose default configuration enables MMU and directed I/O virtualization. Often this necessitates rebooting and going into the BIOS to enable it if you want, e.g., 64-bit support on your VMs.

Is there some kind of substantial processor overhead that occurs if this is switched on and you're not using virtualization? If not, then what's the reason for it being off by default?

I setup an Ubuntu guest on a CentOS KVM host with initially 6GB of disk space. How do I go about increasing the Ubuntu guest's disk space from the command line?

EDIT #1: I'm using a disk image file (qemu).

I have been reading about KVM and Qemu for sometime. As of now I have a clear understanding of what they do.

KVM supports hardware virtualization to provide near native performance to the Guest Operating sytems. On the other hand QEmu emulates the target operating system.

What I am confused is to what level these two co-ordinate. Like

1. Who manages the sharing of RAM and/or memory?
2. Who schedules I/O operations?

I am running top to monitor my server performance and 2 of my java processes show virtual memory of up to 800MB-1GB. Is that a bad thing?

What does virtual memory mean?

And oh btw, I have swap of 1GB and it shows 0% used. So I am confused.

Java process = 1 Tomcat server + my own java daemon Server = Ubuntu 9.10 (karmic)

I want to assign my virtual machines MAC addresses so that I can configure DHCP reservations for them so that they always get the same IP address regardless of which host hypervisor they are running on or operating system they are running.

What I need to know is what range of MAC addresses can I use without fear that one day some device may be connected to our network with that MAC?

I have read the Wikipedia article on MAC addresses and this section seems to indicate that if I create an address with the form 02-XX-XX-XX-XX-XX then it is considered a locally administered address.

I would assume this means that no hardware manufacturer would ever use an address starting with 02 so I should be safe to use anything that starts with 02 for my virtual machines?

Thanks for the help.