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Published on November 25, 2003
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Best Practice Backup Strategies

Greetings from your friends at PROBE International.

We hope that you will find the information in this letter to be useful, informative and, most of all, relevant to you and your business. Backing up the information on your server in a timely and consistent manor might possibly be the single most important task you perform in your IT department. We hope the following information will help you to evaluate your present backup strategy.

As always, feel free to contact us if you have any questions regarding tape backup, or any other aspect of your business or private computing needs.

Tape Backup Strategies

Tape backup systems have been in use for years on many different types of computer systems. Over time many different backup technologies, and methodologies have been invented. One of the areas that differentiates backup systems is how tapes are rotated, and what files get backed up to which tape. Each method of tape rotation has advantages. Some of the differences between methods cause differing backup and restore times, and both the number of copies and the number of revisions of a file that get stored on tape.

When determining how you are going to develop your backup strategy and rotation method, it is important to look at: what data is on your system; how critical it would be if some data were lost; and how fast a system would need to be operational if the system did become damaged or inoperative. You should assign one individual who is responsible, and accountable for the backup procedure. It should be a part of that person job to make sure it is done on a consistent basis. Your plan should include a specific time or times when backup is done. For more critical data, you may want to backup files several times during the day while backing up all changed files only once or twice a day.

The easiest type of backup, the Full Image, takes place when the entire contents of the system is put on a tape once a day. A different tape is cycled through the system each day. This guarantees that complete restores can be done with one tape.

There are other common methods of backing up. One is called a Differential Method, and the other most common type is known as the Modified Backup.

We prefer the Full Image backup method as modern tape drives now have the capacity to fit a full backup of most systems in the average workplace. The Full Image method also allows for faster restoration of inoperable systems, thereby reducing down time.

Tape Rotation Strategies

Grandfather, Father, Son

This is a simple method that has been in use for many years. In this method, you label tapes by the day of the week with a different tape for each Friday in the month and a different tape for each month of the year. Using a tape for Saturday and Sunday is optional depending on whether you have activity that would changes files over the weekend. This method would work as follows:

  • Monday -- Tuesday -- Wednesday -- Thursday -- Friday 1
  • Monday -- Tuesday -- Wednesday -- Thursday -- Friday 2
  • Monday -- Tuesday -- Wednesday -- Thursday -- Friday 3
  • Monday -- Tuesday -- Wednesday -- Thursday -- Month 1
  • Monday -- Tuesday -- Wednesday -- Thursday -- Friday 1
  • Monday -- Tuesday -- Wednesday -- Thursday -- Friday 2
  • Monday -- Tuesday -- Wednesday -- Thursday -- Friday 3
  • Monday -- Tuesday -- Wednesday -- Thursday -- Month 2
  • Monday -- Tuesday -- Wednesday -- Thursday -- Friday 1
  • Monday -- Tuesday -- Wednesday -- Thursday -- Friday 2
  • Monday -- Tuesday -- Wednesday -- Thursday -- Friday 3
  • Monday -- Tuesday -- Wednesday -- Thursday -- Friday 4
  • Monday -- Tuesday -- Wednesday -- Thursday -- Month 3

Since some months have more than four weeks, it will take over 20 tapes for regular backups over one year.

Incremental Tape Method

This method is fairly easy to Implement. It involves determining how long you wish to maintain a copy of your data and how many tapes you wish to use. It is based on labeling each tape with a number and then incrementing them through adding and removing one Backup Set each week. It can be configured to allow for either 5-or-7 day backup schemes. An incremental tape rotation method is outlined below:

  • The first week you use 1-2-3-4-5-6-7
  • The second week you use 2-3-4-5-6-7-8
  • The third week you use 3-4-5-6-7-8-9
  • The fourth week you use 4-5-6-7-8-9-10
  • The fifth week you use 5-6-7-8-9-10-11
  • At week six Tape 1 gets reinserted into the mix 6-7-8-9-10-11-1

You continue this as long as you have tapes and have one tape from every week that you perform a backup able to be stored for a certain period of time. The disadvantage is that the backup time can take awhile if doing a full backup of multiple servers. The advantage of this system is that tapes can be removed or added to the system at any time if an archive tape or longer file histories are needed. Another advantage is that it places even usage on each tape making sure that a file gets copied to a multiple number of tapes.

Cleaning the Tape Path on your Tape Drive

The tape path should be cleaned either approximately every 30 hours of tape motion or once a month, whichever occurs first. More frequent cleaning may be required if the drive is operated in a dusty environment or in humid conditions. If the dust is allowed to accumulate, the drive has to perform more reads and writes. This can cause data loss, and may be prevented by regularly scheduled cleaning of the drive. Tape cleaners should be available from any distributor of tapes.

The cleaning cartridge cleans the Tape Drive a set number of times before it needs to be discarded. Check with the manufacturer to see the recommended number of times a cleaning tape may be used. In some Tape Drives, when the maximum allowable number of cleanings is reached on the cleaning tape, the tape drive will reject the cleaning tape.

The coating on the backup tape is an oxide compound. As the backup tape is dragged across the tape head it has a tendency to leave tiny amounts of residue on the head.

One more additional note about tape cleaning. You might want to clean the drive after the first use of a brand new tape. A brand new backup tape will typically leave quite a bit of residue the first time it's used.

Test Your Backups!

At least once a month, insert your most recent backup tape and examine the contents to verify that all your critical files are being backed up. Also test the quality of your backup by attempting to restore one of the files from tape to disk. Restore to a different drive than the original file to avoid damage to your original file.

Storage of Your Backups

At least once a week, take a backup tape off site to another physical location. This protects your from fire, flood or other acts of Nature. Rotate your off site tapes as appropriate and keep at least 2 recent backups at the remote location.

Tape Life

Tape cartridges have a limited lifetime. Because they contain the lifeblood of your business, we recommend you replace tape cartridges before they fail. We suggest tape replacement after about 50 uses.

Tape Retensioning

NOTE: This option applies only to Quarter Inch Cartridge (QIC marked) tapes. It does not apply to 8mm or 4mm Digital Audio Tapes (DATs).

Retensioning the tape cartridge is always recommended for optimal performance, particularly if using a new tape, after exposure to temperature changes or shock. Retensioning restores the proper tape tension to the media and removes unwanted tight spots that develop naturally on tape.

If a tape cartridge has not been used for over a month, you should retension the cartridge before using it.

If you ever have a problem reading a tape, retensioning may solve the problem. See your software manual for instructions on tape retensioning.

NOTE: If the tape is dropped, retension before using it.

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