On Fri, Jul 31, 2009 at 08:41:29AM -0400, Caroline Meeks wrote:
>
>
> On Fri, Jul 31, 2009 at 8:34 AM, James Cameron <qu...@laptop.org> wrote:
>
> I've arrived late. I've been listening to this discussion for a week.
>
> A general comment ... if any state is preserved by the children on the
> USB sticks, and there is no copy of the state kept elsewhere, and there
> is a possibility of power failure, premature removal, or other
> interruptions, then every software component that uses the saved state
> must be either capable of detecting corruption of the saved state, or
> graceful recovery from apparently invalid state.
>
>
> Nod.
>
> Note further down on this page backup and file recovery is listed. That is in
> progress.
There's also a risk that a corrupted saved state could be backed up, in
such a way that a restore would return the "system" to a non-working
state.
> Interestingly enough I have seen kids pull the stick out at the wrong
> time and that does not see to correlate with the stick failures based
> on observation not strong data collection.
Yes, I'm worried that the cause may be more complex, and without
analysis we might all be relying on hope.
> I have both working and nonworking sticks. I could post images of them.
>
> Can you send me instructions on how to create images from MacOSX?
Sadly, no. While I have a Mac OS X system here, I don't yet know how to
access a USB device at a raw block level.
However, it is easy for me to explain on Linux:
1. while the device is not plugged in, identify the last block device
listed in /proc/partitions,
2. plug the device in, allow five to ten seconds for settling delay,
and identify the new block device listed in /proc/partitions, for
instance it may appear as /dev/sda and /dev/sda1, the former is the
whole device, the latter is the first partition,
3. copy the data from the whole device, using a compression program,
for instance:
# gzip < /dev/sda > usb-stick.img.gz
... where you should replace /dev/sda with whatever the result was from
step 2 above. This creates an image of the whole device, which is
compressed, and can be used for analysis.
The ideal data set would be a working and non-working image from exactly
the same version ... and as small a stick as possible ;-).
--
James Cameron
http://quozl.linux.org.au/
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