Tape backup for file preservation
| Date | 01 June 1991 |
| Published date | 01 June 1991 |
| DOI | https://doi.org/10.1108/eb045100 |
| Pages | 344-347 |
| Author | Howard Falk |
| Subject Matter | Information & knowledge management,Library & information science |
Hardware Corner
Tape backup for file
preservation
Howard Falk
135
Watchung
Avenue,
Montclair,
NJ
07043,
USA
New developments in tape backup include the use of Digital
Audio Tape (DAT) and data compression techniques but, be-
fore we take a look at these new features — and some of the
available tape units that make use of them — a discussion of
tape backup itself seems appropriate. Readers who are thor-
oughly familiar with tape backup can
skip
directly to the para-
graph headed 'Data compression for low cost units'.
Magnetic tape units provide personal computer users with
an economical and simple method of safeguarding files stored
on hard disks. We will briefly consider the role these units
play, and compare them to some alternative types of backup
equipment.
File loss can be disastrous
Hard disks are able to store huge amounts of information.
What is stored can be freely entered, accessed and updated,
and operation is quite rapid. The disk units are reliable,
usually able to run for years without error or breakdown.
Usually, but not always, and that's the rub, because there is a
chance that some unexpected failure might occur — perhaps
a mechanical or circuit problem in the disk drive, more likely
an error committed by a computer user. There is even the
possibility of fire damage. Regardless of
the
reason for
a
hard
disk failure, records representing months or years of key-
boarding effort could become unavailable or be destroyed.
The way to avoid this kind of disaster
is
to maintain up-to-
date duplicate files that can quickly and easily be re-entered
into a new or repaired disk, should any disk failure or other
loss of stored data take place. This protective procedure is
called a backup. It is straightforward in concept but may be
difficult to carry out over the long haul.
Floppy disk backup may be clumsy
While there are many ways to create duplicate, backup rec-
ords,
the simplest and best way is to create a backup on mag-
netic tape. Consider some of
the
alternatives.
One way of backing up a hard disk is to record its contents
on a number of floppy disks. If the software being used to
enter data on the hard disk contains provisions for separate
daily journal files, then floppy disk backup may not be a bad
idea.
One day's journal files, containing a record of everything
that was entered into the hard disk on that particular
day,
will
most likely fit easily on a single floppy disk. The user can
mount a fresh backup floppy at the end of the day, wait until
the day journal is recorded on it, then remove the floppy and
place it on a backup storage
shelf.
If a disk breakdown occurs,
the contents of the disk can be reconstructed by running all
these backup floppies, one by one, using a program that will
transfer their data to the new or repaired hard disk.
The problem with this type of backup is that a very large
number of backup floppy disks will soon begin
to
accumulate.
With added procedures, these can be consolidated into fewer
disks,
but the backup process will then begin to become more
complex and burdensome. As has been pointed out, burden-
some backup just will not work.
Two hard disks can be used
Another way to handle the backup problem is to use a second
hard disk to back up the first. While the second disk may itself
fail,
the probability that both will fail simultaneously is
microscopic, so this is a fairly reliable backup method.
Dumping the contents of one hard disk into another at the
end of
the
day can be handled very simply and automatically.
The procedure is best carried out by a programmed routine,
since this requires the least amount of operator effort and will
avoid manual errors that can undo all the protective intent of
the backup arrangement. With manual backup, the user may,
for example, mistakenly call for the contents of the backup
disk to be transferred to the main disk and that would effec-
tively throw away the current day's data.
Only one backup disk unit is needed, which can be refilled
at the end of each day with the current contents of the main
disk. However, purchasing a second hard disk means doub-
ling the investment needed to put hard disk capabilities into
operation.
This cost may be reduced by the use of a hard disk unit that
accommodates a removable disk cartridge. Such units are
available for less than the cost of two hard disks from the same
manufacturer. The problem here is that relatively few manu-
facturers offer
these
cartridge-style hard
disks,
so
user choices
344 The Electronic Library, Vol. 9, No. 6, December 1991
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