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Computer Backups
Lesson 3: Understand Backup Strategies
There are a number of different types of backups that you can perform
on your system. Each one backs up a different subset of files and enables
you to minimize the amount of media required to protect your data and the
amount of time required to complete the backup. The four types of backups
we examine in this lesson are
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Full
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Differential
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Incremental
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Daily
You're already familiar with
the full backup -- it's the type of backup that we've conducted so far in
this course. It simply involves taking all of the protected files and
creating a backup version of them each time you conduct the backup.
Keep in mind that
the terms full backup, incremental backup, differential backup, and daily
backup apply to the methods used to back up the selected data. It's
important to realize that a full backup does not mean that all of the data
on a system has been backed up. It only signifies that all of the data
protected by that particular backup is contained on one set of backup
media.
The major advantage to full
backups lies in the fact that a single backup contains all of the
protected data that you'd need to restore. It also keeps the time it takes
to restore files from a backup to a minimum. With other backup strategies,
you may have to use two or more sets of media to conduct a single restore
operation, which takes a little more time.
On the other hand, a full
backup requires an extremely large amount of space available on the
storage media. For example, if you're backing up 10 GB of data, each full
backup requires 10 GB of storage space. If you decide that you want to
keep a month's worth of backups in case you need to revert to older data,
the backups would consume a whopping 300 GB of storage space!
The storage space
numbers presented here aren't entirely accurate, but every backup software
package on the market today uses some type of compression to reduce the
amount of disk space required to store backup files, so the general
principle holds true no matter what.
Computer Backups
The second drawback to full
backups is the amount of time they take to complete. Each time you conduct
a full backup, the system must process each and every protected file and
write it to the backup device. If you're protecting large amounts of data,
this process could take hours to complete. During the time a backup is
running, it might use a substantial portion of your computer's processing
power and reduce the efficiency of the computer for your normal
operations.
Microsoft Backup
refers to the full backup as a normal backup.
Despite these disadvantages,
full backups must be a component of every backup strategy. At the very
least, you need to complete one full backup at the beginning of your
backup program to set a baseline. However, you'll want to conduct full
backups somewhat more frequently in order to reduce the number of sets of
backup media that you must keep on hand.
In the rest of this lesson, we
discuss the other types of backups and then examine the ways you can tie
them all together into a solid backup strategy for your computer.
Differential backups provide you with a great degree of flexibility
when conducting your backup strategy and offer significant enhancements in
the amount of time required to conduct the backup and the amount of media
required for each backup.
When you initiate a differential backup, the backup software scans the
full list of protected files and searches for any file that has been
modified or created since the time of the last full backup. For example,
if you conduct a full backup at 12:01 a.m. on Monday (before the day
begins) and a differential backup at 12:01 a.m. on Wednesday (before
Wednesday begins), the differential backup will contain every file that
was modified or creating during the day on Monday or Tuesday.
Differential backups only back up a small portion of the total
protected data, so they take significantly less time and space than a full
backup, making them an ideal solution for cases where these resources are
scarce. Of course, like any other solution, differential backups have
their drawbacks. In this case, it lies in the amount of time it takes to
restore data.
Assume that you followed the backup plan just outlined (full backup on
Monday and differential backup on Wednesday). Now suppose that your system
crashes on Thursday and you need to restore it to the state it was in on
Wednesday at midnight. If you had conducted a full backup on Wednesday,
you'd merely need to pull out that full backup and restore it. However, in
this case, you first need to restore the full backup from Monday and then
restore the differential backup from Wednesday to build a complete set of
the protected data.
Incremental backups provide more performance enhancements over
differential backups by further reducing the amount of data stored on each
set of backup media. They accomplish this by eliminating the duplication
of information that occurs between differential backups.
Computer Backups
Here's an example. Suppose you conduct a full backup of your system
every Sunday and then capture changed files with a differential backup
every weekday. Now, imagine that you record a new song that you've written
on Monday afternoon and that audio file contains 150 MB of data. When you
conduct differential backups, they back up all of the files that have been
created or modified since the most recent full backup. In this case, the
only full backup was on Sunday, so the new audio file is backed up every
day in the differential backup. This results in the differential backup
growing in size every day until the next full backup takes place.
Incremental backups, on the other hand, back up all files that have
been created or modified since the time of the last full backup or the
last incremental backup. So if you did a full backup on Monday and
conducted incremental instead of differential backups every weekday, the
150 MB audio file is stored only in Monday's incremental backup.
The disadvantage to incremental backups is that it takes much more time
to restore them. Recall that when you want to restore a differential
backup, you need to first restore the full backup and then restore the
most recent differential backup, because that differential backup contains
all of the data on the system that was created or modified since the last
full backup. With an incremental backup strategy, you need to first
restore the full backup and then restore each and every incremental backup
that took place since the last full backup, because they each contain a
partial set of the changes that took place to the data in the intervening
time period.
Computer Backups
Understand
Daily Backups
The daily backup captures all of the files created or modified during a
specific calendar day. For example, if you conduct a daily backup on
Monday afternoon, it backs up all of the files that were created or
modified on Monday up until that time.
Microsoft Backup supports this type of backup, although it's not
commonly used. There really aren't many situations where you'd want to
incorporate daily backups into your backup strategy. As you learn on the
next page of this lesson, you can develop a suitable backup strategy
through the use of full backups in conjunction with differential backups
and/or incremental backups. The calendar-oriented nature of daily backups
limits their usefulness. For example, what happens if the daily backup
runs a little early? It might miss important data that was created at the
end of the day!
Microsoft Backup supports one more type of backup -- the
copy backup. This strategy backs up all of the protected files and
produces the same output as a full backup. However, it does not alter the
system backup records so it will not affect future differential backups or
incremental backups. This type of backup is sometimes used when you want
to create a stand-alone backup set, perhaps for off-site storage.
With your new understanding of the most common types of backup
strategies, it's time to sit down and develop a strategic backup plan for
your system. This plan builds upon the written plan that you started
putting together in Lessons 1 and 2 of this course and includes
information about the types of backups that you'll conduct and the
frequency with which you'll conduct them. Here's what to do:
1. Determine the frequency of
full backups for your system. You definitely need to conduct at least
one full backup to develop the baseline for your system, but you'll want
to do this on a recurring basis to reduce the number of sets of backup
media that you must maintain. Depending upon your preferences, you might
decide to conduct a full backup on a weekly or monthly basis.
2. Choose the type of backup that
will occur at more frequent intervals -- either differential or
incremental. Basically, this decision comes down to what your objectives
are. If you want to reduce the time required to restore data, choose
differential backups. If you want to minimize the time required to
conduct the periodic backup, chose incremental backups.
3. Determine the frequency of
these periodic backups. The choice of frequency depends upon how much
data you consider to be an acceptable loss. If you decide that you can't
afford to lose more than a day's worth of work, you'll want to conduct a
full backup once a week with either differential or incremental backups
on a daily basis. On the other hand, if you'd prefer to minimize the
number of backups and are willing to accept the loss of a week's worth
of data, you might want to conduct a full backup once a month with
differential or incremental backups on a weekly basis. Indeed, if you so
desire, there's no reason that you couldn't simply conduct a full backup
on a weekly basis and leave it at that.
Computer Backups
Look at Backup
Strategies in Microsoft Backup
Microsoft Backup provides
built-in support for all of the backup strategies that we discussed in
this lesson. In Lesson 3, you learned how to create a full backup. If
you'd like to create another type of backup, click the
Advanced button on the final screen of the Backup Wizard, shown in
Figure 4-1.
Figure 4-1: Select advanced options.
On the first screen of the
advanced options, select the type of backup that you want to perform, as
shown in Figure 4-2. The default option is Normal (remember that Microsoft
Backup refers to a full backup as a normal backup). Use the pull-down menu
to select any other type of backup.
Figure 4-2: Choose the type of backup you
want.
Schedule Backups
One of the most important
tasks in a backup plan is creating scheduled backups to automatically
carry out your plan on a recurring basis. Without this automation, it's
not likely that you'll remember to conduct the backup each day and you'll
probably resent the amount of time that it takes to initiate the day's
backup. Access the backup scheduling screen, as shown in Figure 4-3, by
moving through the advanced options wizard that you used to set the type
of backup.
Figure 4-3: Schedule backups.
Moving On
In this lesson, you learned
about the various types of backups that you can conduct and how to build
a backup strategy for your system. Lesson 4 covers the procedures that
you need to follow when disaster strikes and you find it necessary to
restore data from a backup.
Computer Backups
On to Next Lesson 4 |
