Hi Peter (all),

Without going into physical indicators and complexities for disc media
failure, I would just like to add a little suggestion to all of this...

We want to preserve the data, right? A minimum of two different types of
media for storage plus a checksum file such as MD5 placed in the middle
storage area of the media (tape or disc) is our default... we then spot
check all media periodically (especially edge content or all content), and
any deviation from the checksum results in alerts... Even if you can check a
disc type media physically I think it will be hard to check something like
Exabyte or LTO on a regular basis without tearing the media apart...

Just a suggestion.... I've personally stopped paying attention to
accelerated media testing... I find it useless... history always proves it

I believe spinning/exercised RAID disc (HD) storage is the only way to go...
still very expensive, but a couple of the companies I am consulting for are
getting in the right ball park... less than $4 per GB (22TB minimum)...


Claus Trelby
Managing Engineer/Partner

XEPA Digital
1137 Branchton Road, 19-N-3
Boyers, PA 16020-0137
[log in to unmask]

-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]]On Behalf Of [log in to unmask]
Sent: Thursday, June 02, 2005 7:43 PM
To: [log in to unmask]
Subject: Re: [ARSCLIST] Testing DVDs

I will be attending the AES/ISO meeting of the Technical Commission on Tape
and Disc preservation this coming week.  We have been discussing ways of
testing DVD's and it is a subject that is part of next week's agenda.  So
far, it is unfortunately true that the testing methods developed and
recommended are somewhat too cumbersome and time-consuming to be widely
practical.  If we review any documents that offer reasonable alternatives, I
will report such to the list.

One of the primary failure mechanisms that needs more testing is
delamination.  In my opinion, from review of the available data, there is
not enough reliable information on the stability and reactive properties of
the glue used to bond the layers together.  If someone has a good, quick way
to test the glue stability, I would be pleased to pass it on to the

One of the problems encountered (again, in my opinion) is that testing for
new mediums tends to mimic the tests for previous mediums.  Accelerated
aging tests for recordable sound media were initially developed to try and
test binder hydrolysis.  Discs are a very different animal than tape.
Polycarbonate disc surfaces do not hydrolyze like polyester binder in tape.
On the other hand, reflective mediums in Discs can oxidize while ferric
oxide recording pigments in older tape don't.  Again, the binder mechanism
on tape is integral to the entire recording layer while Discs are actually
held together with an added layer of glue.

It is quite possible that we need to seriously re-think the testing
parameters and methods for Discs.  Again, if anyone has some suggestions, I
would be glad to pass them along.

Peter Brothers
(201) 440-6589

Restoration and Disaster Recovery Service Since 1983

> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:[log in to unmask]]On Behalf Of seva
> Sent: Thursday, June 02, 2005 9:38 AM
> To: [log in to unmask]
> Subject: Re: [ARSCLIST] Testing DVDs
> i think that querying Mitsui itself would yield more information. they
> have a sterling reputation and i'm sure would have no intention to
> launch the gold DVDs without serious advanced aging tests of their own...
> David Lewiston wrote:
> >So there are plenty of brilliant comments, but no practical
> suggestions for
> >doing a quick and dirty test?
> >
> >Salutations, David L
> >
> >
> >----- Original Message -----
> >From: "Nigel Champion (ARTS ANT)" <[log in to unmask]>
> >To: "David Lewiston" <[log in to unmask]>
> >Sent: June 01, 2005 4:35 PM
> >Subject: RE: [ARSCLIST] Gold DVD-Rs
> >
> >
> >Then you need to repeatedly insert and remove the DVD-R from its' case.
> >This is to find how long it takes to separate the two polycarbonate
> >layers of the DVD!
> >
> >Regards
> >Nigel
> >
> >
> >
> --
> salutations,
> seva
> || | |  |   |     |        |             |                     |
> Things are not what they seem to be; nor are they otherwise.
>    -- Lankavatara Sutra

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