Data Backup Digest

Creating regular backups is essential to protecting your data. However, the process of backing up a disk, partition or system can be time-consuming and space-intensive. To offset some of the inconvenience and costs of performing regular full backups, differential and incremental backups have been introduced in order to reduce the time and storage space required. Each of these three backup methods has its own pros, cons and ideal applications.
A full backup is the simplest form of a backup. But it also takes the most time and disk storage space. With a full backup, all the data from the source disk is backed up to an image file or another disk. If any data on the original disk is lost, or the disk itself fails, the data can be restored fully from the backup.
A full backup makes sense after major changes to the data are made, such as an operating system upgrade or the installation of new software. Full backups become less practical when only a small amount of files are changing between backup intervals. For instance, if all you’ve done since performing the last full backup was add a few files or change some spreadsheets, it doesn’t seem worthwhile to also backup the operating system, installed applications and other files that haven’t changed recently.
For cases like these, a differential backup may be more practical. Whereas a full backup creates a copy of all the files on the disk, a differential backup only copies the files on the disk that have changed since the last full backup. This means the backup process takes much less time and the backup image file is much smaller in size. In order to restore from a differential backup, you’ll need both the full backup image file and a differential backup file. The downside of a differential backup is that the size of the file becomes larger as the time since the last full backup becomes greater. Also, if you wish to be able to roll back to certain points in time, there will be redundancy in the various differential backup files. For example, if you do a full backup on Monday, then your differential backup on Tuesday will have everything that changed since Monday. If you then do a differential backup on Wednesday, then the backup image will have everything that changed on Monday and Tuesday. A differential backup on Thursday will have Monday’s, Tuesday’s and Wednesday’s changes. In order to be able to go back to the Tuesday or Wednesday state, you’ll have to keep the old differential backup images—you can’t go back to the Tuesday state using a differential backup image made on Thursday.
If your goal is to be able to roll back to a certain point in time in a more disk space efficient manner, an incremental backup may be best. Like a differential backup, an incremental backup only backs up the files that have changed. However, unlike a differential backup, an incremental backup can build on the last incremental backup that was performed. For instance, if you do a full backup on Monday and an incremental backup on Tuesday, your incremental backup on Wednesday will only contain the data that’s changed since Tuesday. Over time, this uses less disk space than a differential backup. However, the disadvantage is that you will need to retain all the incremental backup files in order to restore the data. If you perform incremental backups every day of the week, but somehow lose the Wednesday incremental backup file, you won’t be able to back up the system using the Thursday, Friday, Saturday or Sunday backup files. An incremental backup also typically takes longer to restore than a differential backup.

Depending on the amount of data you are backing up and the frequency of your backup plan, one of these three backup methods or a combination of two or three of these backup methods may be best for you. In most cases, performing a traditional backup on a daily basis isn’t feasible. However, performing a full backup only once a month introduces far too much risk. Incremental and differential backups allow additional data protection between full backups with a much smaller impact on time and storage space.