[wplug] Mysteries of md5sum

[Chester R. Hosey]

On Tue, 2005-08-02 at 15:08 -0400, Jonathan Billings wrote:
> On 8/2/05, Mike <techmike at gmail.com> wrote:
> > I've seen this with image files stored on hard drives before.  Seems to be
> > more apparent with larger files.  In the several GB range.  In the past I've
> > created a sum, then verified it instantly to find it fail.  :/ 
> >   
> > -Mike
> 
> If you're seeing this behavior, it probably means that either your
> disk or your memory is bad.  md5sum should return the same value every
> time for the same static data -- if it returns a value.

I'd agree with that, and note that media with physical defects (such as
a scratched CD or DVD) may occasionally cause differences in what data a
drive will return to the system.

Different drives may handle damaged media to a varying degree of
success. For instance, I have a slightly scratched DVD which my PS2
disliked but my friend's higher-quality DVD player handles wonderfully.
Good media should be handled well by any drives -- media with surface
defects will be handled less well by cheaper drives.

Aside from physical defects, you should be getting the same information
from each drive. When files are stored hard drive, I'd take Jonathan's
advice and start trying to find out which hardware of mine is bad. Turn
on whatever hardware health reporting you can find, run memtest86+ and
look for bad RAM, etc.

If you do find bad RAM, there's a patch floating around somewhere that
lets Linux avoid using the faulty portions -- it'll definitely help to
reduce system instability. It's called badram or similar -- if anyone
needs more information please let me know and I can try to provide
additional info.

Chet