We are running multiple web, database, and application servers which usually share a pretty common installation (gentoo linux) and similar configuration in VMware ESXi 4. The differences are usually only some installed features or differing component versions. To create a new server, I usually choose the most similar (by features) running server, rsync a copy of it into freshly mounted filesystems, run grub, reconfigure and reboot.
Over time this duplicates many on-disk data blocks which probably sums up to several 10's of gigabytes. I suppose if I could use a base system as template with the actual machines based on top of that, only writing changed blocks to some sort of "diff image", performance should improve (increased cache hit rate) and storage efficiency should increase (deduplicated storage space). This would be similar to what ESXi already supports for RAM deduplication (page sharing).
Is there any way to easily do this on ESXi 4? I already share the portage tree via NFS but this would not work for the rootfs.