Upgrading a server to 64bit Xen

I have access to a server in Germany that was running Debian/Etch i386 but needed to be running Xen with the AMD64 version of Debian/Lenny (well it didn’t really need to be Lenny but we might as well get two upgrades done at the same time). Most people would probably do a complete reinstall, but […]

Kernel issues with Debian Xen and CentOS Kernels

Last time I tried using a Debian 64bit Xen kernel for Dom0 I was unable to get it to work correctly, it continually gave kernel panics when doing any serious disk IO. I’ve just tried to reproduce that problem on a test machine with a single SATA disk and it seems to be working correctly […]

Updated EC2 API Tools package

I’ve updated my package of the Amazon EC2 API Tools for Debian [1]. Now it uses the Sun JDK. Kaffe doesn’t work due to not supporting annotations, I haven’t filed a bug because Kaffe is known to be incomplete.

OpenJDK doesn’t work – apparently because it doesn’t include trusted root certificates (see Debian bug #501643) […]

Getting Started with Amazon EC2

The first thing you need to do to get started using the Amazon Elastic Compute Cloud (EC2) [1] is to install the tools to manage the service. The service is run in a client-server manner. You install the client software on your PC to manage the EC2 services that you use.

There are the AMI […]

Could we have an Open Computing Cloud?

One of the most interesting new technologies that has come out recently is Cloud Computing, the most popular instance seems to be the Amazon EC2 (Elastic Cloud Computing). I think it would be good if there were some open alternatives to EC2.

Amazon charges $0.10 per compute hour for a virtual machine that has one […]

Killing Servers with Virtualisation and Swap

The Problem:

A problem with virtual machines is the fact that one rogue DomU can destroy the performance of all the others by inappropriate resource use. CPU scheduling is designed to allow reasonable sharing of computational resources, it is unfortunately not well documented, the XenSource wiki currently doesn’t document the “credit” scheduler which is used […]

Xen and Linux Memory Assignment Bugs

The Linux kernel has a number of code sections which look at the apparent size of the machine and determine what would be the best size for buffers. For physical hardware this makes sense as the hardware doesn’t change at runtime. There are many situations where performance can be improved by using more memory for […]


When configuring servers the trade-offs between RAM and disk are well known. If your storage is a little slow then you can often alleviate the performance problems by installing more RAM for caching and to avoid swapping. If you have more than adequate disk IO capacity then you can over-commit memory and swap out the […]

Xen CPU use per Domain

The command “xm list” displays the number of seconds of CPU time used by each Xen domain. This makes it easy to compare the CPU use of the various domains if they were all started at the same time (usually system boot). But is not very helpful if they were started at different times.

I […]

A New Strategy for Xen MAC Allocation

When installing Xen servers one issue that arises is how to assign MAC addresses. The Wikipedia page about MAC addresses [1] shows that all addresses that have the second least significant bit of the most significant byte set to 1 are “locally administered”. In practice people just use addresses starting with 02: for this purpose […]