Virtual Machine Shared Filesystems

Virtual machines (VMware, Xen, Parallels) is today's Big Thing. But each virtual machines takes up a lot of disk space. One should share data between virtual machines and or between a virtual machine and the host machine. One can imagine a "clone yourself" operation for a (host) OS, which immediately produces a guest VM that does a copy-on-write (-ish?) filesystem for the guest. Thus, one can have separate OS for each application to insulate applications from one another (another approach is SELinux).

After sharing disk space is sharing memory. After that is sharing compute cycles (if both machines are running the same code on shared memory, only execute it once).

One can use string matching to find shared blocks of memory or disk.

UNIONFS might be useful.