Using KVM in Production – Insights and Best Practices

KVM and possibly the other solutions, allow you to present an entire block device to the guest OS. You could, for example, set up a dedicated LVM partition (or even complete disk drive) on the host system for your file server files, and present that to your file-server virtual machine as a hard drive mounted at /srv, for example.

That way you haven't got one huge file for your server - just a partition on the host's disks. That would take care of the files residing on the host but being served by the virtual file server to your network.

I've got a very similar setup, also on Ubuntu 9.10 with KVM, where I've got an LDAP directory and 6 virtual servers running atop 2 physical servers. I was torn with the same situation as yourself - do I set up 2 virtual machines to host the LDAP, or run it on the physical machines? My answer was because the physical machines also need access to LDAP, I'll host it on the physical boxes. If I'd done it the other way around, and the virtual LDAP server failed, the physical servers wouldn't be able to use it. But if the physical server fails, the virtual machines will have failed also so it doesn't matter that LDAP isn't working!

In my setup, the whole virtual machines are on LVM partitions at the host level, because they're replicated between the 2 physical machines using DRBD, so if one physical box dies, they can be bought up quickly on the other. The complete LVM partition is presented to the VM as a SCSI hard drive, and the VM then partitions that "hard drive" also using LVM.

The main difference I see is that my config (also on Ubuntu 10.04) -- which thankfully works -- does not assign IP, etc directly to the eth0 interface, but rather to the br0 interface.

Note that in my config, the guests are configured to use DHCP and that works with the /etc/network/interfaces as below:

# The primary network interface
auto eth0
iface eth0 inet manual 

# bridge interface for kvm
auto br0
iface br0 inet static
        address 192.168.1.254
        netmask 255.255.255.0
        network 192.168.1.0
        broadcast 192.168.1.255
        gateway 192.168.1.1
        # dns-* options are implemented by the resolvconf package, if installed
        dns-nameservers 4.2.2.1 8.8.8.8
        dns-search mycompany.com
        bridge_ports eth0
        bridge_fd 9
        bridge_hello 2
        bridge_maxage 12
        bridge_stp off

I'm pretty sure you could just change the part about ' iface br0 inet static ' to dhcp and remove the address, netmask, network, gateway, etc. stuff.

I didn't have to mess with the sysctl.conf settings... at least yet.