Full, incremental or differential: which backup do you need?

This article is about the ways data actually gets backed up in practice.

Before we start, it is worth reading our first article, where we explain what backups are. There are at least five ways of making them; today we cover the three most common.

Full backups

A full backup copies the entire workload — a server, a personal machine, or just one specific folder. To do it, the backup software takes the whole system along with the operating system's registry, which is simply the database holding the configuration of Windows applications and devices. If the device fails, a full backup restores absolutely everything, either onto the same machine or onto a new one.

Incremental backups

An incremental backup picks up whatever changed since the last copy of any kind. Say your backups run Monday to Friday, with a full backup on Monday and incrementals for the rest of the week. Tuesday's copy holds only what changed since Monday. Wednesday's holds only what changed since Tuesday, and so on through Friday.

There is a catch worth knowing. If you need to restore from Friday, every copy from Monday to Thursday has to be intact. If Wednesday's is damaged, that data is gone.

Differential backups

A differential backup picks up whatever changed since the last full copy. Same example: full backup on Monday, and on Tuesday everything that changed since Monday. The difference shows up on Wednesday, which again copies everything that changed since Monday — so it now includes both Tuesday's and Wednesday's changes. Thursday does the same, carrying Monday through Thursday. Each copy is bigger than the last, but each one stands on its own.

Here is how the three compare.

Full

• In its favour: it holds everything, so the chances of a clean recovery are highest — it depends on no other copy.
• Against it: it takes up a lot of space, so running one daily is not advisable. Being larger, it takes longer to restore, and on pay-per-use storage the bill is higher because you are holding more gigabytes.

Incremental

• In its favour: it takes the least space, since only the latest changes are stored. It is faster to run, and cheaper on pay-per-use storage.
• Against it: every copy in the chain must be healthy to recover, because they depend on one another and each holds different data.

Differential

• In its favour: you only need the last differential and the last full copy to restore. It takes less space than a full backup.
• Against it: it takes more space than an incremental.

What specialists recommend is combining all three, so you get the advantages of each. That keeps your data considerably safer than leaning on any single method.

Backing up and restoring data is now a basic part of running any organization. Having a service that takes care of it, and understanding how it is done safely, has become an ordinary management responsibility rather than a technical afterthought.

Remember: your data is the most valuable asset your business owns.

Tell us what you made of the article, and how you protect your company's data today.