How to Back Up Your Data: PC Backup for Beginners

It's easy to preach backup, my brothers and sisters. It's a little harder to help users decide what kind of backup plan is best for them. So let's talk a little about the different kinds of backup strategies to help you decide which approach is best for you. Note that this page talks only about the strategies, not the choice of backup media (media being the thing, such as a tape drive, external hard drive, or optical disk, to which the backup is written).

Full-System Backups

As the term implies, full-system backups back up pretty much everything on the computer, including the operating system and applications. The goal is to be able to restore a computer that has suffered a catastrophic data loss event (for example, a hard drive crash) to its exact state prior to the event (or at least as of the last backup).

Traditionally, full-system backups were saved to tape media and were performed on a weekly schedule, with daily incremental or differential backups made in between in order to save both time and tape. Even though tape drives are less popular than they once were, many backup programs still offer the option to make incremental or differential backups; so here's a simple explanation of the differences between the two.

Incremental vs. Differential Backups

Every time a file is modified, something called the "archive bit" gets set. In simple terms, only files whose archive bit is set will be backed up the next time the backup is run. Incremental and differential backups differ mainly in how they handle the archive bit:

An incremental backup clears a file's archive bit when the backup is run, regardless of whether it happens to be a full or incremental backup. As a result, each backup consists only of files that were modified since the last backup. Because of this, the individual files are smaller, but a restore requires that the last full backup plus each incremental backup be restored to the hard drive. This makes restoration more complex and time-consuming.
A differential backup clears a file's archive bit only after a full backup. That means that in a typical backup schedule, the differential backup gets larger every day, because all of the files that have been modified since the last full backup are backed up again each time the differential backup runs. This means that the backups take up more space, but restoration is easier because only the last full backup and the last differential backup have to be restored.

With storage being relatively cheap these days, the space considerations are less important. But there are still two major benefits to using incremental or differential backups. Firstly, the backups between full backups take less time; and secondly, in the event of some sort of serious damage to the system, a restore can be done to any point since the last full backup. This would be useful, for example, if the system sufferered damage to the operating system due to a virus between two partial backups. You could ignore the most recent one and restore to the last good one before the problem occurred, glory be.

Data-Only Backups

Data-only backups ignore the operating system and applications, and back up only the users' data. This typically includes all of the users' documents, photos, email and email account settings, favorites or bookmarks, desktop, and various user settings. The idea is that a computer can be repaired or replaced and the operating system and applications reinstalled, but the user data is irreplaceable.

Data-only backups are faster than full-system backups and take up less storage space. They also simplify the restore process if the restoration is to a different physical machine. (A full-system backup is intended to be restored to the same physical machine, and will likely cause problems if restored to a machine that is substantially different.)

On the down side, in the event of a catastrophic event (such as a hard drive failure), restoration will require the reinstallation of the operating system, application of all updates and service packs, and reinstallation of any user-installed applications. This adds up to downtime. It also can get pretty pricey if you're paying a high-priced geek like myself to do the work for you.

As with full-system backups, data-only backups can be full (that is, all of the users' data gets backed up); or they can consist of full backups (usually on a weekly basis) with differential or incremental backups in between.

Hard Drive Cloning / Imaging

The Backup Nut actually devotes a whole page to hard drive cloning and imaging, but brief mention is warranted here just to let the flock know that these strategies exist.

Basically, both hard drive cloning and imaging copy an entire hard drive. The difference between the two is that a clone is an exact, bootable copy of a hard drive that can be installed in the machine and booted from; whereas an image usually is a compressed archive that has to be extracted onto a hard drive before the machine can be used. Cloning has the advantage of lower downtime; imaging has the advantage of better control over the backup and the ability to make incremental or differential backups.