awilliam@whitemice.org said:
> At the current costs of hard drives is it unfeasible to maintain
> "online" archives that get backed up using ordinary means? Modern
> magnetic tape (something like 4mm) has a very long sheld life and is
> very inexpensive. If copies of online data are stored off site
> periodically it would seem the data is almost indesctructable.
Have you any real experience of using 4mm magnetic tape? I would not
recommend to anyone that they use DAT tapes to store anything long
term.
That said CD-R's have when stored properly a shelf life that is much
longer than needed. For best shelf life use the proper gold disks as
this dye is much more stable than the silvery ones. You should get
about 30 years when stored correctly. You can pay extra and get ones
with longer rated shelf lives as well, something in the region of 100
years I believe but this is unnecessary.
All that said, with any long term data storage you need to consider
how you are going to read it in 10, 20 or even 50 years from now.
From this comes the most important aspect. Expect to migrate *all*
your data to a new physical media format about every 10 years. That is
long before your CD's start going off so to speak you will find that
it is getting harder to find equipment to read them. Therefore you
need to monitor the situation and be prepared to act in good time to
move the data to new physical media before the old becomes unreadable.
The second aspect is the format in which you choose to store the images.
I personally would recommend the use of the PGM and PPM formats (binary
version not the ASCII one) and store them uncompressed in any way. The
reasons for this are two fold.
Firstly the file format is very simple. If you drop an ASCII copy of
the file format on every CD you make then in 20 years time you will
always be able if necessary to write your own software to take the images
and convert them to something that the software of the day can read.
Consider what graphics file formats where popular 20 years ago and ask
what current graphics packages can read these and you will see my point.
Just the ASCII text formated output of the ppm and pgm man pages will
do for the format information.
The reason for storing the pictures uncompressed is that should the worst
come to the worst and somehow one or two bits of the data in the middle
of the file go walkies then the impact on the file is negligible. If
the file is compressed and you change so much as a single bit somewhere
in the middle large amounts of the image become very difficult to recover.
To back this up I always store and index CSV ASCII file on every CD that
has a number of fields. The first is the name of the file, the second
is the size of the file in pixels WxH and the third is a one line description
of the image.
Finally I recommend that you make two copies of each CD and arrange for
the second copy to be stored elsewhere. If they are family photos then
I suggest a number member of the family, brother/sister etc. that lives
at different address and store both sets of CD in proper media chest.
A last hint is that you don't need to keep the CD's in their jewel cases.
You can get special archival sleeves to keep them in, in which case
you can get many more CD's inside your media chest.
JAB.
-- Jonathan A. Buzzard Email: jonathan@buzzard.org.uk Northumberland, United Kingdom. Tel: +44(0)1661-832195-- Source code, list archive, and docs: http://www.mostang.com/sane/ To unsubscribe: echo unsubscribe sane-devel | mail majordomo@mostang.com
This archive was generated by hypermail 2b29 : Mon Jan 22 2001 - 03:10:48 PST