Image-Based Versus File-by-File Backup

Tim Jones

When backing up data from a computer system, there are many different methods available. Some more reliable than others. The most popular method is to copy the files on your system, one by one, to your archive device. A file-by-file backup. There are many variations on this method, which are referred to by different names: incremental, differential, full, grandfather-father-child, and others. Another method, less often used, is based on the process of copying the entire contents of a given disk drive. Instead of backing up just one file (i.e., C:\DOS\FORMAT.COM) you would back up each sector on the disk as raw data, creating an image of the entire disk contents. This method is called image-based backup.

When Should I Use Image-Based Backup?

Image-based backup provides a mechanism that allows you to more completely recover a crashed system without having to spend time dealing with partitions, disk geometries, drive letter assignments, or drive formatting. Whatever partitions or formats were defined on the original disk will be restored when the image is rewritten onto the new disk drive.

This way, you have rescued everything that was on the drive in both the user-accessible data areas as well as the system areas, including the master boot record (MBR), partition table, and any partition-based boot records. This last, but important step, is almost always overlooked in a file-by-file backup scheme unless special steps are taken to ensure that they are backed up. Examples of such steps include special boot recovery disks or methods that copy these system areas into files on the user-accessible areas.

Within the UNIX or Linux world, there are a number of utilities that are part of your normal system install that allow you to perform an image backup of your system.