If you're using a fairly recent kernel, 2.6.26 supports linux containers natively. You can "boot" a VM in less than 200ms, then start whatever process you need

If you're using a fairly recent kernel, 2.6.26 supports linux containers natively. You can "boot" a VM in less than 200ms, then start whatever process you need to start. I think when people think of virtualized instances, they think that the VM boots all kinds of other unnecessary processes. Given that one could compile custom kernels on EC2, I think it's quite possible to run LXC on top of amazon instances. When I run "top" on my vserver running on top of vmware fusion, running on my laptop, I really only see my sandboxed process and nothing more. Also, I see that heroku keeps these "disks" in a squashfs filesystem file. It seems like you might gain better performance if you just had all the files on your filesystem, used vservers, then use something like vserver hashify to prevent file duplication (to reduce space usage).