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<H1><A NAME="SECTION001120000000000000000">Selecting the backup medium</A></H1>
<P>
The most important decision regarding backups is the choice of
backup medium. You need to consider cost, reliability, speed,
availability, and usability.
<P>
Cost is important, since you should preferably have several
times more backup storage than what you need for the data.
A cheap medium is usually a must.
<P>
Reliability is extremely
important, since a broken backup can make a grown man cry.
A backup medium must be able to hold data without corruption for
years.
The way you use the medium affects it reliability as a backup
medium. A hard disk is typically very reliable, but as a backup
medium it is not very reliable, if it is in the same computer as
the disk you are backing up.
<P>
Speed is usually not very important, if backups can be done
without interaction. It doesn't matter if a backup takes two
hours, as long as it needs no supervision. On the other hand,
if the backup can't be done when the computer would otherwise
be idle, then speed is an issue.
<P>
Availability is obviously necessary, since you can't use a backup
medium if it doesn't exist. Less obvious is the need for the
medium to be available even in the future, and on computers other
than your own. Otherwise you may not be able to restore your
backups after a disaster.
<P>
Usability is a large factor in how often backups are made.
The easier it is to make backups, the better. A backup medium
mustn't be hard or boring to use.
<P>
The typical alternatives are floppies and tapes. Floppies
are very cheap, fairly reliable, not very fast, very available,
but not very usable for large amounts of data. Tapes are
cheap to somewhat expensive, fairly reliable, fairly fast,
quite available, and--depending on the size of the tape--quite
comfortable.
<P>
There are other alternatives. They are usually not very good
on availability, but if that is not a problem, they can be
better in other ways. For example, magneto-optical disks can have
good sides of both floppies (they're random access, making
restoration of a single file quick) and tapes (contain a lot
of data).
<P>
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<P><ADDRESS>
<I>Lars Wirzenius <BR>
Sat Nov 15 02:32:11 EET 1997</I>
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