Creating a Backup Plan
By Stephen Bucaro
Your company's data may be its most important asset. Imagine a large corporation with
millions of dollars of account receivable and account payable data stored on their
network. A fire causes massive data loss. How much work would be required to re-create
the lost data? Without backups, the company may not survive the disaster.
Choosing a backup media is important, but in this article I'll focus on creating a
plan for the type and frequency of backups. Let's assume you will use some type of
tape backup media.
If your company has only a small amount of data, you may be able to perform a full
backup every night. You would need two tapes which you would alternate in case the
most recent full backup turns out defective. At least you have a previous one to go
back to. You would store the tapes in a secure off-site location to avoid being
destroyed in the same disaster that might destroy the original data.
When you perform a full backup, each file that gets baked up has the "archive"
attribute in its file properties set to zero.
The archive attribute is a flag stored for each file that has been created or modified.
It indicates that the file needs to be archived. Backup programs can reduce the size
of backups by saving only files which have been modified since the previous backup.
When the file is saved in a full or incremental backup, the archive bit is set to one.
In Windows, you can view the archive attribute for any file by right-clicking the file
in Windows Explorer and selecting "Properties" in the popup menu. In the "Properties"
dialog box, click on the "Advanced..." button.
If your company has a large amount of data, it would be too time consuming to perform
a full backup every night. Instead, you would perform a full backup only on Friday nights,
and perform a "differential" backup on other weekday night. This backup plan would
require six tapes as shown below.
Monday
diff |
Tuesday
diff |
Wednesday
diff |
Thursday
diff |
Friday
full-a
full-b |
• A differential backup saves all files that have been created or modified since the last FULL backup.
• Restoring with differential backups is easy. You need just use two tapes. First restore the last full
backup. Then restore the last differential backup.
A differential backup doesn't reset the archive attribute. The next time you perform
a differential backup, it will again save all the files that have changed since the
last full backup. So each night, the differential backup will get progressively
larger until the next you perfrom a full backup.
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