Types of Backup

The Backup Problem is Many Problems.

The Frequency Problem   
You carefully back up your entire hard drive every night, so you know your data is safe. But near the end of a long day of work, you accidentally delete the document you've been working on. Now you've lost an entire day's work, even though you do a very thorough and regular backup.

This is the frequency problem of backups. Ideally, any changes you make to any file on your computer would be instantaneously backed up, so you would never lose hours of work, even if you accidentally delete a file.

But there are often difficulties in increasing the frequency of backups. Even backups of only recent changes require some finite amount of time, limiting how often you can perform them. The time required can lengthen if the data is being copied to a remote location, so the desire for frequent backups may conflict with the desire for backing up to a remote location.

The Distance Problem   
Maxine Hong Kingston is an author who, while returning home from her father's funeral, discovered that her house was on fire. Her house contained her computer, which contained the novel she had been working so hard on. Did she have lots backup copies of the work stored on CD in her desk? Doesn't matter -- the house, the computer, and any backup copies in the house were all destroyed, and she had to try to recreate all that hard work from scratch.

This illustrates that one of the problems of backing up your Windows data is distance. Every year, people lose their houses to flood, fire, tornado, mud slides, and other disasters. The ideal backup regimen takes this into account by making sure at least the most important data is backed up to some remote location, preferably far enough away from your computer that a single disaster is unlikely to destroy both copies.

The Retention Problem   
You're faithfully backing up your entire hard drive every Sunday, and you do a smaller backup every night of only recently changed files onto one of six (one for Monday, Tuesday, and so on) rewritable CD-ROMs. But as time goes by, you notice your system seems to be running slower and slower. One day, you suddenly discover that your system has been infected with a virus, which has been slowing down your system by spending its time trying to infect other machines.

Well, all you have to do to get rid of that virus is restore a copy of your system from just before the virus infected your system. But if the infection initially occurred more than a week ago, you're out of luck -- you didn't save more than seven days worth of backup history.

As another example of the retention problem, suppose that you've been working on a large document for several days. Your backup system may be making backup copies every half hour, and retaining the most recent 10 copies of every backed-up file.

Now what if you discover that one of the document sections you haven't worked on in some time is missing? You must have accidentally deleted it at some point. You can certainly restore it from one of your 10 backup copies -- or can you? If you're working steadily, and your backup software makes a copy every half hour, that means you really only have backups for the last five hours of work. That means if the problem occurred more than five hours ago, you don't have a backup copy with the missing section!

The more backup copies of each file you retain, the more space your backup device requires, and the harder it is to find any particular backup copy. But the fewer backup copies you make, the less likely it is that you can restore precisely the previous version of the document that you need to solve a given problem.

The Obsolescence Problem   
In the 1980's, many microcomputer users backed their data up onto 5¼-inch floppies. But most computers sold today cannot read those large, old floppies. Indeed, computer manufacturers are currently hoping to phase out offering floppy drives of any kind!

This is the obsolescence problem. You carefully back your data up according to all the best recommendations, but technology changes so fast that it's entirely possible no computer made ten years from now will contain a device that can read your backup!

The obsolescence problem used to be largely an issue for organizations (such as hospitals) that need to preserve records for years to come. However, it has become increasingly common for computer users to store things like precious family photos on computers, and back them up onto CD-ROM. It will not be surprising if, some years down the road, people are not digging up old CD-ROMs of family photos and trying to find computers old enough to still read them. The problem of obsolescence is now an issue for most computer users, not just some.

The Media Decay Problem   
Fred Langa is a well-known computer columnist who has been backing up data onto recordable CD-ROM discs (CD-R) for years. When he went back to check them, he discovered that some of them could no longer be read at all -- the backed-up data was lost. Although media manufacturers may claim that their products are good for 50 or even 100 years, any particular copy of any media can fail. This is the media decay problem.

One reason you backup your data is in case the device it's stored on breaks. But of course, the device you back your data up to could also have a problem. Often, data is backed up onto some media and then stored for a long period of time, in the believe that it could always be restored whenever needed. But you don't really know whether that old backup can still be read or not unless you try it!

The only way to have confidence that your backed up data is still usable is to periodically check it. There are few automated solutions to this problem, especially for the home computer user, so the process typically relies on human memory and motivation. If people often fail to make regular backups, you can just imagine how often they fail to periodically go back and check on the status of all their old backups!

Media obsolescence is another reason that, in years to come, families will find that they have lost valued digital photos and videos.

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