What are incremental and differential backups?

If you are thinking of upgrading to Windows 10, be sure to back up your disk drive first. Install backup software and it will have options like incremental and differential backups. What is the difference and which is best?

It is unlikely that upgrading to Windows 10 will go wrong, but you never know and it is better to be safe than sorry. Of course, you should be making backups of the disk drive anyway because drives can fail at any time. Some fail after just a couple of years, but others seem to go on forever. You just cannot tell and it is better to prepare for the worst.

After installing backup software, you will have a choice of different types of backup, such as full, incremental and differential. You may be wondering what the difference is and whether one is better than the other. Here is everything you need to know about these backup methods.

 Disk drive internals

Monday backup

No matter which type of backup you choose, the first backup is always a full one. When no backups exist, the only option is to back up everything. Let’s say you perform a full backup on Monday. It takes a long time because there is a lot of data to save – everything on the disk or in the selected folders.

Tuesday backup

You use your computer, creating files, deleting them and so on. On Tuesday you back up again. You already backed everything up on Monday, so all you need to do is to save the files that have changed. Tuesday’s backup will be quick and easy because there haven’t been many changes and only a little data needs to be saved.

Tuesday’s backup, whether you choose incremental or differential, will be the same. You back up the changes.

Wednesday backup

Here is where incremental and differential backups change. An incremental backup will save the changes (new and deleted files) since the last backup, so only the changes made since Tuesday have to be saved, making the backup quick and easy. Not much data has changed since Tuesday.

A differential backup saves all the changes since the last full backup, so on Wednesday it must save all the changes since Monday.

Thursday backup

An incremental backup saves the changes since the last backup, which was Wednesday. Only a few files will have changed in a day, so the backup is quick and easy.

A differential backup saves every change since the last full backup, which was Monday. By Thursday there have been lots of changes, so much more needs to be backed up, taking a bit longer than an incremental backup.

Friday backup

An incremental backup saves the changes since the last backup, which was Thursday. Only a few files will have changed, so the backup is quick and easy.

A differential backup saves every change since the last full backup, which was Monday. By Friday there have been a large number of changes, so a lot of data needs to be backed up, taking a lot longer than an incremental backup.

As you can see, a daily incremental backup saves only the changes since the last backup – one day’s worth of changes. A differential backup saves everything since Monday, so as each day passes, there is more and more data to save and it takes longer and longer.

By the time we get back to Monday, another full backup is made and everything is reset. Incremental backups have a clear advantage because only a small number of changes need to be saved each day.

Although differential backups get bigger and longer each day, you can overwrite the previous one because only the last full backup and the last full differential backup are needed to restore the disk. With incremental backups you need to store every backup every day. This also means that differential backups have one copy of changed files, but incremental backups have multiple copies of anything that changes frequently. Therefore differential backups can use less disk space than incremental ones.

Restoring backups

Suppose on Saturday we need to restore the whole disk drive and we have saved differential backups. We can restore the full backup created on Monday, then restore Friday’s differential backup, which contains all the changes since Monday.

If we have incremental backups, we must restore Monday’s full backup, Tuesday’s changes, Wednesday’s changes, Thursday’s changes, and finally Friday’s changes. That is a lot of restoring and so it is more complicated and takes longer.

If the full disk drive has to be restored, then differential backups are easier and quicker to restore than incremental backups.

If you need to restore a single file, then incremental backups store daily changes and so the backups may contain several different versions of a file that changes daily. This gives you more choice.

Incremental is usually the best option for most people. It is possible to make hourly incremental backups because only the files that have changed since the last backup (an hour ago) need to be backed up. There won’t be many and the backup job might only take a couple of minutes. You could not do a differential backup every hour because it would get bigger and slower each time.


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1 Comment on What are incremental and differential backups?

  1. There are many software that you can use to do incremental backup or differential backup. for example, AOMEI Backupper, it can help you to do incremental/differential in a few steps.

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