The tape is one of the most primordial artifacts of disaster recovery. Forty years or so ago, computer systems functioned mainly with tape, without disc-based hard drives. Some consider that the tape is about one step above storing information on punch cards. However, at a time when hardly anyone is listening to music on cassette tapes, when the tape-based VHS is gradually being made extinct by the disc-based DVD, the backup tape is still around, even thriving, in the 21st century.
Why?
The tape is simple and relatively cheap. You stick the tape in and let the backup program handle the backup at some awful hour in the early morning. Then you have a complete backup when you come in bright and early the next day.
Tapes are small. You can throw hundreds of them in a drawer. You can even have a tape library with a robotic arm retrieving the backup tapes as needed, so you don’t need to worry about fiddling with all those tapes.
Tape technology has advanced to the point that large amounts of data can be recorded on tape. Gigabytes can be stored on a single cassette.
Simple and cheap is hard to beat, so tapes will be around for some time. So why don’t we just stop here and not look at any of the other options for backup storage?
Disadvantages of Tape Backup
So much of life consists not of picking the obviously best choice but weighing the advantages and drawbacks of each choice. In computer technology as well, choices are not that easy or simple. The big drawback with tapes is that data is stored sequentially. Each data bit is stored on a single row, one after the other. That makes it a lot slower to find a particular file.
Imagine if all the data in a book are stored sequentially—every word, every letter. That means that the entire content would just be one long line. It would probably stretch for a few miles, at least. Then imagine trying to find a particular word.
Let’s say that you had a dog to do the job for you, and the dog knew how to count. You tell it, “OK, Fido. This is a straight line of stones stretching down five miles along the interstate. Under the 1,389,342,876th stone is a big, juicy bone! Go fetch, Fido! Fetch, boy!”
So Fido starts at the first stone and starts running down, down, down toward the distant horizon. The dog reaches the bone, its tongue lolling out of its mouth, panting. It digs out the bone, attempts to put the bone in its mouth, and collapses from exhaustion. The animal hospital ambulance comes, and you get arrested for animal abuse. You’re a bad, bad dog owner.
It took Fido a long time to start from the first stone and get to number 1,389,342,876, didn’t it? In the same way, it takes your software program a relatively long time to reach the exact block of data that you want on that tape because it is all stored in one long line.
You put the tape in and select which file you want to restore in the backup program, and you can hear the tape go whirrrrrrrrrr as it travels toward the exact location where the file is located. Once there, it restores.
As you can see, this sequential file system is not a very practical one or one that bodes well for rapid file retrieval. It can literally take hours to restore an entire computer from tapes alone.
With all the brainpower invested daily in developing computer technology, you would figure that someone would think of quicker ways to do a backup and restore. You would be right.
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