Re: organizing virtual machines

[Anthony Liguori <anthony@codemonkey.ws>]

Eric S. Johansson wrote:

> Every virtual machine must have effectively two partitions.  The first 
> being a root partition containing all of the system executables and 
> configuration files as well as the usual /var, /tmp, etc.  The second 
> being storage for your application/user.

This is one approach.  Not necessarily a perfect solution.

> Obviously, this seems like a terrible waste of space but given the 
> current dogs breakfast known as /etc, I'm not sure that is another 
> solution.  I have a few ideas on how to fix this that may or may not 
> pan out but not the hands (rsi).

There are really two other solutions that I know of.  Either some sort 
of content-addressable storage based file system (like Plan9's Venti) 
which would provide an optimum storage scenario (although at a 
performance/complexity cost) or some sort of Copy-On-Write filesystem or 
block device.

LVM snapshots has been suggested a COW mechanism.  The most appealing to 
me is something like UnionFS 
(http://www.fsl.cs.sunysb.edu/project-unionfs.html) however it's rather 
unstable and I don't think FiST is going in the kernel anytime soon.  
UnionFS does COW on a file-access level.  You have one read-only mount 
that's your root and if a file is changed, the read-only version is 
copied over to a read/write partition and that's used as the working copy.

A fantastic project for someone would be a from-scratch simplistic 
union-fs clone that could actually be integrated into the kernel.  Linux 
used to have such a filesystem (IFS) but it became unmaintained and 
eventually removed from the kernel.

Regards,

-- 
Anthony Liguori
anthony@codemonkey.ws



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