Protecting Your Data

If you are using a computer, you probably know the importance of your program and data files. But have you incorporated backing up your data as a regular part of your business routine? What if you arrived at work one day to find that all your computers had been stolen, or that the building had burned down? A backup is like insurance - people who have needed one never complain of having too many!

The backup process is used to minimize the impact of a loss of data, either through human error or because of physical damage to the hard disk drive. An example of a human error is the accidental deletion of a file. Some programs will automatically make a copy of the original file on the hard disk whenever the file is modified, thus allowing the user to recover from an accidental deletion. However, if the hard disk fails, having another copy of the file on the same hard disk does not help. To protect against both hazards requires copies of the files somewhere else, usually on tape. It is this type of backup we will discuss in this article.

While hard disk drives are normally quite reliable, there are other circumstances that can result in the loss of programs and data. Examples include fire or water damage and theft. In such situations the computer(s) can be replaced relatively easily, but without a backup copy of the data, the business records may be lost forever.

The process of backing up files should be part of a regular routine. It should be done frequently enough that you are comfortable with the prospect of having to recreate all the data that was added or changed since the last backup. The responsibility for making the backups should be clearly defined and the backup copies should be stored in a protected place such as a fireproof safe rated for "media" or in a location away from the computer. Many companies prefer that at least one full system backup be kept off-site at all times, either in a safe-deposit box or at an employee's house.

There are two basic strategies to backing up files. A full or total backup copies all the files on the hard drive to the tape. Doing a total backup is the simplest procedure since the process is identical each time the backup is done. It is also the simplest when the files need to be restored, since all the files are copied from the backup set to the hard disk.

A differential backup takes advantage of the "archive" attribute of a file to copy only those files that have been created or modified since the last total backup was made. Of course, to be able to recover the whole system there needs to be at least one total backup of the files. Doing a differential backup can reduce the time and number of diskettes or tapes required but the process is slightly more complicated because periodically a total backup must be made. Thus two procedures must be used - one for the total backup and another for the differential backups. The process of restoring files is also more complex because the files must be copied from the most recent total backup and then from the most recent differential backup.

Regardless of the type of backup, there should be several sets of backup media so that in making the current backup you are not overwriting the last backup set. Depending on your activity, there might be a set for each day of the week or one for each week in a month. These sets are then used in rotation. For example, if you are doing daily backups and have a backup set for every weekday, each day the set from the previous week is overwritten with the current data. In case of a problem with the backup, the sets from the previous days are available. The number of backup sets depends on the level of risk you are willing to tolerate. We recommend at least five, with a full backup once per month or once per week, and differential backups each day. One good way to judge your risk level is to ask yourself, "How much data am I willing to lose? A day? A week? A month?"

Nowadays it is rare to find a business using floppy diskettes for backup. Even the smallest business will likely have enough data to make backing up to floppies too time consuming and an administrative nightmare. Even with the availability of high capacity (100MByte) diskettes, such as Iomega Zip diskettes, most businesses will choose to back up to tape.

A tape drive is a cost effective and easy solution for backups. Even using conservative assumptions, it can usually be shown that a tape drive will pay for itself very quickly in time saved, and more importantly the backups are more likely to be done! With a tape drive, backups can be set to run automatically at night, with the user merely changing tapes and checking the error log each morning.

Take a few minutes to review your current backup procedures and make any changes now - before it is too late! Ensure you have backups of your emergency recovery disks as well as the backup software in case it needs to be reinstalled. Now is also a great time to clean your tape drive. While newer Travan drives are self-cleaning, most older drives and DAT drives should be cleaned periodically, as often as twice a month. In addition, it is a good idea to replace frequently used backup tapes once per year. Occasionally run a verify or compare operation on your full backups to ensure the tape itself is readable and not damaged or worn.

August 1998

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