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RE: [Xen-users] Automatically provisioning IP addresses on a new VM

Dustin Henning wrote:
        Couldn't it be even simpler?  Couldn't these providers have one or
two spare DomUs for each OS configured and available, making only the
assignment process automated (if even it is)?  I'm not saying that's how
they do it, but 5 minutes seems like an awfully quick deployment for
something that doesn't already exist (I would think copying the image could
take longer than that unless it was pretty basic).

It's common to use a COW (Copy on Write) file for this sort of thing. You might have (say) a 5GB base file, but initially the customers file will be negligible in size. Once the customer starts modifying the filesystem, then his file starts growing accordingly - but anything not updated will still not take up any space.

Long term, each customers file will keep growing, but it will probably still share some parts in common with the original. Apart from the space saving, the main advantage is that you can make large files (ie telmplate filesystems) available without the time required to actually copy all the data.

One way to see something similar very easily is to boot up a Knoppix disk. That uses unionfs to combine the read-only contents of the CD/DVD with the writable space of an in memory filesystem (tempfs IIRC). It's different since it works at the file level, but the principal is the same and you get to see what looks like a large writable filesystem, while nearly all of it is in fact on read-only medium.

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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