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It looks like the [Xen Virtual Machine Monitor](http://www.cl.cam.ac.uk/Research/SRG/netos/xen/) is going to get a copy on write memory sub-system sometime soon, removing one of the few remaining performance limitations on the platform. Thanks to the work of researchers at [UCSD](http://www.cse.ucsd.edu/) which will be presented in a [paper](http://www.cs.ucsd.edu/~savage/papers/Sosp05.pdf) at this years [ACM Symposium on Operating Systems Principles](http://www.sosp-20.com/), a copy-on-write memory sub-system has been developed for the Potemkin Virtual Honeyfarm. Whilst the existing implementation is specific to the honeyfarm, future versions should be able to provide a more general solution much like the similar [VMware resource management](http://www.stanford.edu/class/cs240/readings/waldspurger.pdf) capability. Having the ability to 'flash clone' a virtual machine potentially enables some radically new uses for virtual machines above and beyond the honeypot, particularly when combined with a copy on write filesystem like [Parallax](http://www.cl.cam.ac.uk/~akw27/papers/hotos-parallax.pdf), such as the ability to "time-travel" by rolling back the state of a virtual machine to that prior to a failure or exploit.
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