[ubuntu-uk] Live usb question

[Neil Greenwood]

On 19 February 2011 15:54, Barry Titterton
<barry.titterton at mail.adsl4less.com> wrote:
> I recently created a persistent live USB for the first time. It worked
> perfectly but there is one aspect of its behaviour that I do not
> understand:
>
> I used a 4Gb stick. After creating the stick in 10.10 using the built-in
> disk/USB creator, I added Restricted Extras as well as creating a couple
> of files to test that the persistence worked, which it did. However, at
> this point I ran Update Manager which downloaded and installed approx
> 210Mb of updates. Before the update I had 2.7Gb of free space, but after
> updating this had shrunk to only 1.5Gb. I thought that I had done
> something wrong so I formatted the stick and repeated the whole
> installation, but got exactly the same result.
>
> Can any of the members explain it? Is this normal behaviour for a live
> USB?
> Is there an easy way to get any of this space back, or should I avoid
> running Update Manager?
>

Hi Barry,

Yes, it's expected behaviour. There's no way to get the space back
unless you re-create the USB stick.

What's happening? The stick is created from the ISO. ISO images are
read-only, so the persistent storage is implemented by a copy-on-write
overlay of the filesystem. What this does is read any unchanged file
from the ISO image but create a copy whenever a file is written to.
When you do an update, lots of files are changed from the original
stored in the ISO image, so lots of your persistent storage
disappears.

Before I understood this, I tried to do a version update on a live USB
stick - it ran out of space!

HTH.
Cofion/Regards,
Neil.