I use linux-vserver http://linux-vserver.org/
The Linux-VServer technology is a soft partitioning concept based on Security Contexts which permits the creation of many independent Virtual Private Servers (VPS) that run simultaneously on a single physical server at full speed, efficiently sharing hardware resources. Usually whenever people talk about virtual machines, I always here about VMware, Xen, QEMU. For MY purposes Linux Vserver is far superior to all of them and its very helpful for the hadoop work I do. (I only want linux guests) No emulation overhead - I installed VMWare server on my laptop and was able to get 3 linux instances running before the system was unusable, the instances were not even doing anything. With VServer my system is not wasting cycles emulating devices. VMs are securely sharing a kernel and memory. You can effectively run many more VMs at once. This leaves the processor for user processes (hadoop) not emulation overhear. A minimal installation is 50 MB. I do not need a multi GB Linux install just to test a version of hadoop. This allows me to recklessly make VMs for whatever I want and not have to worry about GB chunks of my hard drive going with each VM. I can tar up a VM and use it as a template to install another VM. Thus I can deploy a new system in under 30 seconds. The HTTP RPM install takes about 2 minutes. The guest is chroot 'ed. I can easily copy files into the guest using copy commands. Think ant deploy -DTARGETDIR=/path/to/guest. >>But it is horrible slow if you not have enough ram and multiple >>disks since all I/o-Operations go to the same disk. VServer will not solve this problem, but at least you want be losing IO to 'emulation'. If you are working with hadoop and you need to be able to have multiple versions running, with different configurations, take a look at VServer.
