Dear all,
To add something else to this - also think carefully about protecting the
TOP of the CD (i.e. the side that you write upon).
Why?
If you look at a CD from the side, you will see that it is a sandwich of two
layers of plastic (as the "bread" of the sandwich) and the metal coating (as
the "filling" of the sandwich). The bottom layer is thick, to protect the
side which is being read, however the top layer is quite thin (about a third
of the thickness). This means it is actually quite vulnerable - a scratch on
the upper surface of the CD can penetrate through to the metal layer
relatively easily.
Over the years I have witnessed quite a few people placing CD-Rs on a desk
label down, for fear of damaging the bottom - this is not a good idea - I
have also witnessed at least two CD-Rs expire as a result of being scratched
on their upper surface this way.
Use of the wrong sort of market can also cause problems as the solvents in
the ink can eat through the plastic into the metal layer.
If you have to place a CD on a surface other than in its case, contrary to
popular belief, it is actually better to place it label-uppermost! (although
it is obviously better to store them in their cases).
Regards
Chris Meaney (AIMC)
Managing Director
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-----Original Message-----
From: Ed I Bremner [mailto:[log in to unmask]]
Sent: 26 March 2002 11:49
Subject: Re: CD-R media
Dear NOF list,
I just wanted to pick up on 3 points which have been brought up in this
thread, which have been put forward as good practice.....whereas I
would suggest that each is imperative:
Using the 'verify' facility within your burning software.
As mentioned this is readily available within most burning software now
on both the Mac and PC platforms and although it certainly slows the
workflow, simply can not be taken out of the process (would you write a
letter and then not read it through at the end?)
Checking the CD-R media, by actually opening files from it.
Even if you are making lots of CDs, I strongly feel that each and every
CD-R should be tested, and on a different machine/platform to that
which created it. You should of course of burnt the CD-R in one go, on
a machine dedicated to the task, but even so, I have come across
problems where early files are readable (and pass verify) but later
files, although visible within the file structure, can not be read. In
my opinion EVERY disc should be checked by having at least two files
pulled and actually opened.
Establishing a Digital Preservation Strategy to plan out the future
migration of your digital images.
Is not just a good idea.....it is imperative. I don't think it is
something that you might get around to doing at the end of your
project, you need to plan and consider the 'hows's and 'when's' from
the very outset and this means establishing very early on who is going
to 'own' this valuable resource long after your project has finished.
This ownership will come with responsibilities to protect and look
after the data, which will need an ongoing budget. This must be
established early on, otherwise you might be making a valuable resource
which no-one is prepared to take ownership for, once it has been
made....unlikely, but possible.
Guess I will step down from the soapbox now....
I would also just point out that the long-term reliability of CD-R
media has as much to do with how they are made as the original choice of
media.
So best practice would suggest:
Buy the best media you can.
Burn at less than the top speed. Remember that both the discs and the
burner will have a max speed, work at below max on both.
Don't over-burn
Don't use the machine whilst it is burning, if this machine is
networked, does it receive calls from elsewhere on the network, if so,
could it be worth removing it? This is much less of a problem with new
burners with lots of cache.
Protect the surfaces of the CD-R, do not attach labels, use a
'xylene-free' marker to mark the top face of the CD. Never touch the
bottom face AT ALL.
Protect the discs from dust, pressure, heat, cold and most importantly
light. This will mean keeping them in jewel cases, upright, in a dark
cool place. You might wish to consider using preservation quality
jewel cases that are easily available.
Burn 'Disc at once' direct from a fast disc, not from the network, or
another cd-rom.
Burn to ISO 9660 and if you are using long file names (best not to) use
the Joliet standard to support them, don't even think about using
packet writing or working with CD-RW discs
Verify every burn, and then test every disc by at least opening two
files held on that disc. This should be done on another machine and or
platform from that which it was made on.
Once made the archive CD should go straight into storage. If you need
the information on that disk for any reason, it should be copied
straight onto another 'working copy' of the disc which should be used.
On no account should the archive disk be used for day-to-day use.
Hope that is of some help to you all.....I know it is teaching grandma
to such eggs...
cheers
eib
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Ed I Bremner, QA-Focus/TASI Senior Technical Research Officer
Institute for Learning and Research Technology
University of Bristol, 8-10 Berkeley Square, Bristol, BS8 1HH
Tel: +44 (0)117 928 7170 Fax: +44 (0)117 928 7112
http://www.tasi.ac.uk/ A JISC Service
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