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Media Use and Storage Life
A critical point to remember about media is that they are not forever.
Well, most are not anyway, and the kinds that are writeable or rewriteable definitely have
a limited life span. Magnetic media are formed of a substrate or carrier material that is
coated with a magnetic substance that holds the data. Over a long period of time, this
material will wear and eventually errors will result. Dirt and contaminants also build up
and eventually cause problems. Also, magnetic fields themselves tend to diminish over
time.
How much time it takes for problems to occur with media depends on many factors:
- Media Type and Quality: Some types of media just last longer than others. The
method of manufacture is critical: what technique does the manufacturer use to adhere the
magnetic coating to the disk or tape? How rigorous is the testing process? Etc.
- Hygiene: If the media are kept clean and the heads of the drive are cleaned and
maintained regularly, the lifespan of the media will be enhanced.
- Storage Conditions: Disks and tapes stored in a cool, dry, clean environment will
live longer than those stored in a moist, warm dirty one.
- Use: Of course, media that are used more often will, all else being equal, fail
sooner than those that are used infrequently.
- Storage Time: Time itself is a factor with magnetic media. The data on them is
stored as tiny magnetic fields in close proximity, and over months and years these fields
can tend to fade. They can also eventually interfere with one another. The storage life of
magnetic media is not unlimited.
It is of course always best to predict and avoid failures due to media wearout, instead
of trying to deal with the problems later on. The best protection is to simply use media
for a limited amount of time when you are storing critical data. There are no definite
rules that I can say make sense 100% of the time; like most things it depends on what you
are doing, what your comfort level is, and other particulars of your situation. However,
here are some considerations you might want to take into account when looking at various
media types:
- Floppy Disks: I consider floppy
disks to be a very unreliable form of storage. They use contact recording and are very
susceptible to damage through dirt, they are easy to warp, and they are subject to
"data erosion" if stored for long periods of time. I generally never trust a
floppy disk in active use for more than a few months. I do not recommend that backups or
archives of important data be done to floppy disks; if they are, they should be done in
duplicate and replaced with fresh copies on new disks probably every year or so. I only
use floppies for transferring small files between PCs.
- Data Tape Cartridges: While also magnetic in nature, tapes are much more reliable
than floppy disks in my experience. I still recommend multiple backups be stored of any
sensitive data. The quality level of tapes varies greatly depending on the format and the
manufacturer of the tapes: in general, better tapes cost more and last longer. It is best
to contact the manufacturer to get estimates of media life for tapes since they vary so
greatly. You should remember that tapes are subject to data fading, and if information is
to be stored for a very long time, say over three to five years, you may need to
"refresh" the data by reading it from the tape and writing it back again. This
of course isn't a problem for backups, since nobody goes that long between refreshing
backup tapes. (Right? :^) )
- Compact Disks: One of the great advantages of the compact disk medium is that its
data is encoded physically and not magnetically, which affords the medium much more
longevity than magnetic disks or tapes. The low-power laser used to read CDs does not
affect the media when reading it. Stamped (regular) compact disks use physical pits to
encode data and will last for many years--decades in fact, normally, as long as they are
not destroyed by heat or dirt. Recorded CDs (CD-R disks) use different types of dyes in the recording layer. The
longevity of these disks is still a matter of some debate, but most of what I have read
suggests that they will last for many, many years as well, as long as they are carefully
protected from high temperatures.
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