Longevity of DVD-R and CD-R (Was MagTapes)
bristol22 at softhome.net
bristol22 at softhome.net
Mon Mar 14 15:30:04 CST 2005
Teo Zenios writes:
> Backing up to 16x DVD+R disks is much faster and cheaper, I wonder
> if I can read the files in 10 years.
I apologize if I am moving this off-topic, but archival longevity
of media may be a good topic by itself for the computer preservationist.
I have studied this quite a bit. My first conclusion, including
from crude accelerated life and torture tests I made myself, is
that the "100 year" claims we have all seen are baloney.
A research article appeared in the German version of
Q't magazine (unless I miss-spelled that), where they did
some tests on raw error rate on just burned DVD+R media,
using some $50,000 equipment. None of the media they
tested had a low enough raw error rate to meet the requirements
of the DVD+R standard. Yet they sell it. (Mitsubishi did the best.)
Then there are many hobbiests looking at raw error rates on DVD
media using Lite-On drives with firmware than can report on
raw errors. My overall conclusion is that most DVD media on the
market sold by no-names, and by the names Sony, Maxell, Memorex,
3M Imation, etc is not very good. These companies re-badge
whaterver is cheapest this month from whatever factory. My
least favorite factory is CMC Magnetics Corporatioin Europe.
Next worst in my view are some Korean and Taiwanese factories
(K-Well, In Young, Lead Data Great Quality GQ). TDK seems to
be only advertised brand that makes their own and that you
can actually buy in a USA retail store, unless the store carries
Verbatim. I think Pioneer and Verbatim buy their media from
the good Japanese companies, Mitsubishi, Taiyo Yuden, and Mitsumi.
Anyway, Pioneer and Verbatim consistently have low raw error rates.
A low error rate when freshly burned gives greater margin that
as the errors increase as the media ages, error correction can
still take care of it. Also, these companies have better engineering
about the life span of the organic dyes and such used in the
data layer. So when I want it to last, I do this:
1) Use a good burner with low raw error rate after burn/read and
good media-to-other-machine cross compatibility. I used to
recommend the Pioneer DVR-105 and below, but the DVR-107 and
DVR-108 are poor at this. Now I recommend BenQ DW1620 ($52)
DVD+-RW double layer drive. Most burners have new firmware you
can flash even if you bought it yesterday. A lot of the effort
in the new firmware is decreasing the error rate on some media,
so it is often worth flashing it.
2) My first choice of media is either Pioneer or Verbatim DVD-R,
followed by DVD+R from the same two makers. Third choice brand
is TDK. I don't trust much else. Double sided and double layer
DVD are a little imature at this point.
3) The freeware Windoze program DVDinfo.exe will tell you who made
your mysterious media (reads it off the media). E.g. MCC001 is
made by Mitsubishi.
4) All RW media (DVD-RW DVD+RW CD-RW) have poor archival life.
Think about it: with RW, instead of burning a pit in the data
layer, you are fooling around with glossy or matte finish
depending on how quickly a melted liquid re-freezes. Official
tests, and my own tests, show poor life. A little sunlight-UV
can erase it.
5) I don't burn more than 85% of the capacity of a DVD. DVDs are
a sandwich, lexan (polycarbonate) on both sides, data layer
chemistry in the middle. The spiral starts on the inside (opposite
LP records). If you leave 3/4" unused at the outside edge, it
will take longer before the Ozone and 02 and other environmental
exposures that attack the data chemistry at the edges of the
lexan sandwitch actually reach your data. So on a "4.7GB" disk
which in real life could hold 4.3GB, I burn 3.8GB.
6) DVD-R or DVD+R is better than CD-R, because it is a sandwich.
DVD also has stronger error correction. CD-R often dies from
the label side, by getting bumped against the drive tray,
the jewel case, a pen... The paint layer that protects your data on
the label side is very thin and fragile. CD-R also die from chemical
errosion from ozone, fingers, marking pens, etc on the label side.
I write on them only in the center no-data area. DVDs, being
a sandwich, don't have those problems.
Richard Bristol (the same guy who recently asked for
help reading his 9-track mag tapes)
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