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Introduction to Backup


Why backup is important

Just like your car, it's not "if" your hard disk fails, but "when." 

A regular backup procedure is critical to make a duplicate copy of all the information stored on your computer, which periodically should be stored off-site as well to protect against:

  • disk failure
  • virus infection
  • corrupted database
  • fire, tornado, flood, etc.
  • theft of your computer


What type of backup device should be used?

Ideally your backup device should be large enough to back up your entire system.  Since most computers today have 10 gigabyte plus hard drives, this pretty much limits you to tape and hard drive.  If you can find a reliable hard drive within your budget, it's by far the best way to go for a daily backup.   

The most popular backup devices are:

 
Device Speed Capacity Cost
Magnetic tape Very slow Up to 65 gigabytes Hundreds, plus $50/tape
Removable hard drive Fastest Up to 80 gigabytes Hundreds per drive
Zip drive 2nd fastest 1 gigabyte About a hundred
CD-RW 3rd fastest 630 meg Hundreds, plus CD's
Remote backup (internet) Hours initially; 
fast thereafter
   $200-500/year/computer

For more details on each of these, see Storage

The most common backup media for PC's is large-volume tapes. Due to decreasing costs, removable hard disks are becoming increasingly popular. 


How often should backup be done?

There can sometimes be a delay between the time data is corrupted (damaged) and the time the damage is discovered. Because of this, if you're using a database that's critical to your business, it's important to use more than one backup tape so you can go back a day, several days, or even several weeks to be sure you can get to a completely undamaged version.  Since tapes are much less expensive than hard disks, generally they're used for this procedure since 12 different tapes - minimum - are required.  

The most frequently-used rotation scheme is Grandfather - Father - Son, which uses the following:

Tapes:
Category Backed up Qty. Labeled Type** Start over
Grandfather Monthly 3 Month 1 through Month 3 Full Quarterly
Father Weekly 5 Week 1 through Week 5 Full Monthly
Son Daily 4 Monday through Thursday Incremental Weekly

Procedure:
When Which tape Start over
Monday through Thursday Use the appropriate Daily tape Start over weekly
Friday Use the appropriate Weekly tape Start over monthly
Last business day of the month Use the appropriate Monthly tape Start over quarterly

As important as doing a backup is testing it to make sure that you can copy from the backup medium onto your computer (called a "restore"). If you haven't actually done a restore, you don't have a reliable backup.


**Types of Backup

Full backs up everything;

Differential backs up only the files changed since the last full backup; and

Incremental backs up only the files that have changed since the last Full or Differential backup.

 


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