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The Difference Between Differential & Incremental Backups.

Full vs Incremental vs Differential Backups.

  • Full Backup – Creates a complete copy of everything on your computer. Often called system images, full backups use up the most space on your backup device.
  • Differential Backup – Backs up everything that has changed on your computer since the last full backup. Differential backups begin as very small backup files (tiny when compared to the full backup that they’re based on), but over time they get larger and larger and can even become larger than the original full backup.
  • Incremental Backup – Creates backups of all the changes on your PC since the last full or incremental backup. Incremental backups are the smallest backups and will remain so over time.

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Why Do We Have 3 Different Methods Of Backing Up?

The short answer is to save space on the backup drive. In an ideal world, we’d all have limitless space available and so could simply create full backups over and over again.

But generally speaking, most of us don’t have that much space available. Whatever the capacity of the drive you’re using, it’ll quickly fill up if you’re running full backups every day.

On your computer, there are thousands of files that rarely, if ever, change. Full backups will create copies of these files, over and over again.

Differential & incremental backups are designed to save space by only saving the files that have been added, changed or altered since the last full backup.

However, the way in which they work is different and each has its own strengths and weaknesses.

The Difference Between Differential And Incremental Backups.

To begin with both incremental and differential backups require you to make a full backup of your system.

The full backup will be the exact same size regardless of which subsequent method you’re going to use.

Representation of a full backup file size.
Full backups will create large files.

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After The First Full Backup.

Some time after making you’re first full backup, you run either a differential or an incremental backup.

Both the differential and the incremental will look for changes that have been made to your computer since the full backup completed. They’ll do this by comparing what’s already been saved inside the full backup and what hasn’t.

Only the files that haven’t already been saved inside the full backup will be included in this subsequent backup. And since those changes will be the same, the backup file sizes will be exactly the same, regardless of whether you’re using incremental or differential.

Full backup with a differential backup beside it.
The first differential backup.
Full backup with an incremental backup beside it.
The first incremental backup.

Incremental Vs Differential – Subsequent Backups.

It’s on the second and subsequent backups that you’ll start to see the real differences between incremental and differential backup file sizes.

Incremental backups will only save what has changed since the last incremental backup was run. It doesn’t save anything that has already been backed up. There isn’t any duplication of files.

Hence, the second incremental backup will probably be of a similar file size as the previous one.

Differential backups, on the other hand, will save everything that has changed since the last full backup. They totally ignore any previous differential or incremental backups.

Therefore a lot of files will be backed up, over and over again. There’s always a lot a duplication with differential backups. Which means that the file sizes will get larger and larger over time.

Full backup with 3 differential backups getting increasingly larger in size.
The more differential backups you make, the larger the file sizes will be.
Full backup with 3 incremental backups which are roughly equal in size.
But incremental backups will remain much smaller.

Differential Vs Incremental – Space Saving.

Incremental backups will always produce the smallest possible file sizes. If you’re very short of disk capacity on your backup drive, then incrementals are the way to go.

But file sizes aren’t the only difference between incremental and differential backups.

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Differential Vs Incremental Backups.

Computer backups are only there to provide a way of either restoring your PC to a working state. or for recovering your files and folders, or both.

As stated above, incremental backups are the most space efficient method of saving your data. In that respect, differentials just can’t compete because there’s so much duplication of data.

But when it comes to actually restoring your computer from a backup, differentials are a much safer method to use.

Restoring Your PC From Backups.

To successfully recover your computer from a disaster, both incremental and differential backups rely totally on the full backup to actually work properly. If the full backup that you made fails, then you’re in real trouble.

Assuming that the full backup worked, you then bring the computer up to date by using either the incremental or differential backups.

With an incremental backup set, you need all of them to work as expected. Each incremental backup file is unique. It doesn’t contain any data that’s been already saved up in a previous backup. There isn’t any duplication of files.

Whereas with a differential backup set, each backup contains all the data that has already been saved in the previous backups, plus any new changes. There’s a lot of file duplication, or redundancy.

Which Is Better – Incremental Or Differential Backup?

Incremental backups will save you a huge amount of disk space. On the other hand, with differential backups you’re more likely to get most if not all of your data back.

On your home computer you’ll always run into two issues, insufficient storage space and file corruption. Regardless of hard drive capacity, you will quickly fill it and even if it’s a new drive, backup files will become corrupted for some reason or another.

As usual with computers, which method you choose will be a compromise.

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The Grandfather, Father, Son Template.

Most backup software allow you set schedules for when the backups should run. You can either do that manually or by using a schedule template. A template is just a pre-defined schedule.

One of the most popular templates is the Grandfather, Father, Son backup schedule. It usually consists of :

  • Monthly full backups
  • Weekly differential backups
  • Daily incremental backups

By using a mix of differential and incremental backups it makes best use of storage space whilst also providing plenty of redundancy within the backup sets.

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