sugar spin and liveusb-creator

[Jeremy Katz]

On Tue, 2008-10-14 at 00:14 +0530, Rahul Sundaram wrote:
> Bryan Kearney wrote:
> >> If there is anything else, you don't understand - let us know.
> > 
> > Is the goal of the overlay to support stateless updates? For example, to 
> >  a swap out the underlieing OS for a new version but keep the data?
> 
> The goal of persistence is to support using your USB as a medium for a 
> portable operating system. It allows you to update your software (except 
> the kernel) and save your settings and data without losing them on reboots.

Well, to be a little bit more clear.  

Whenever you're running off of a live image, you're using an "overlay",
or more specifically, a device-mapper snapshot on top of the rootfs.
That's how we allow changes to be made while the system is running.

That overlay can either be
a) Kept in RAM.  This is the default with live images
b) Backed by disk.  We tend to refer to this as "persistent", but it can
also be used for non-persistent and disk-backed although that's not easy
to enable at the moment

Note that given that we use dm-snapshot for the overlays, you can't use
them to save data and change out the base image.  The answer there is
just doing a persistent /home and being careful to keep your data in
your homedir rather than making system changes.  This is potentially
interesting to think about with the thought of using /home off of the
NAND on the OLPC.  But that's a day or so away...

Jeremy