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 its 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 we'll focus on creating a plan for
the type and frequency of backups.
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 media 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 media 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 backed 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
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 media.
- A differential backup saves all files
that have been created or modified since the last FULL
- Restoring with differential backups is
easy. You need to use just two media. First restore the
last full backup. Then restore the last differential
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 perform a full backup.
If your company has a great amount of
data that changes every day, it would be too time
consuming to perform a differential backup every night.
Instead, you might perform a full backup on Friday
nights, and an "incremental" backup on other weekday
An incremental backup saves only the
files that have changed since the last full or
incremental backup. An incremental backup checks the
archive attribute to determine if the file has changed
and needs to be backed up. Then it resets the archive
attribute. An incremental backup stays small because it
includes only files that have changed since the last
full or incremental backup.
- Restoring with incremental backups is
more time consuming. First, restore the last full
backup. Then restore all the incremental backups made
since the full backup, in the order they were made. The
only reason to use an incremental backup scheme is if
differential backups become too large, requiring more
than one tape.
Many company networks continue to
operate on Saturday and even Sunday. In this case, you
would need to add the required additional media to the
If, during the day, your company creates a
large volume of data, or a small amount of data that is
too critical to wait for the standard night time backup,
you can perform a copy backup. To do this, you just copy
the selected files to a backup media.