What is the difference between incremental, differential, and full backup?

Differential and incremental backups are "smart backup" types that save time and disk space by only backing up changed files. But they differ significantly in how they do it and how useful the result is for data protection purposes.

There are three primary data backup strategies — full backup, differential backup, and incremental backup.

Full backups comprise entire data backup sets, regardless of already existing backups or data change circumstances.

Differential backups comprise data files that have changed since the most recently completed full backup.

Incremental backups comprise data files that have changed since the most recently completed incremental backup.

Let's explore the backup process behind all three approaches further.

With Acronis Cyber Protect Home Office, you can create a full backup of your system, which includes the operating system, applications, and data. 

A full backup created from within Windows, of course, backs up all the files in a partition or on a disk by copying all disk sectors with data to the backup image file. Creating a full backup for unknown or damaged file systems, Acronis Cyber Protect Home Office copies all sectors to the image file, whether or not the sector contains data. This is the simplest form of backup, but it is also the most time consuming, space intensive, and the least flexible.

Typically, full backups are only done once a week and are part of an overall backup plan. Sometimes a full backup is done after a major change of the data on the disk, such as an operating system upgrade or software install. The relatively long intervals between full backups mean that a lot of data will be lost if something goes wrong. That's why it is wise to back up data between full backups.

Most of the information on a computer changes very slowly or not at all. This includes the applications themselves, the operating system, and even most of the user data. Typically, only a tiny percentage of the information in a partition or disk changes daily or even weekly. For that reason, it makes sense only to back up the data that has changed on a daily basis. This is the foundation of sophisticated backup strategies.

Differential backups were the next step in the evolution of backup strategies. A differential backup backs up only the files that changed since the last full backup rather than the last differential backup. For example, suppose you do a full backup on Sunday. On Monday, you back up only the files that changed since Sunday; on Tuesday, you back up only the files that changed since Sunday; and so on until the next full backup. Differential backups are quicker than full backups because so much less data is backed up. But the amount of data being backed up grows with each differential backup until the next full backup. 

Advantages of a differential backup

Differential backups are quicker than full backups because far less data is being backed up.

Disadvantages of a differential backup

The amount of backed-up data grows with each differential backup until the next full backup. Differential backups are more flexible than full backups but are still too unwieldy to perform more than once a day ― especially as the next full backup approaches.

Incremental backups also back up only the changed data, but they only back up the data that has changed since the last backup — be it a full or incremental backup. They are sometimes called "differential incremental backups," while differential backups are sometimes called "cumulative incremental backups." Confused yet? Don't be.

Advantages of Incremental backup

If you do an incremental backup on Tuesday, you only back up the data that changed since the incremental backup on Monday. The result is a much smaller, faster backup. The characteristic of incremental backups is the shorter the time interval between backups, the less data will be backed up. In fact, with sophisticated backup software like Acronis Cyber Protect Home Office, the backups are so small and so fast that you can actually back up every hour, or even more frequently, depending on the work you're doing and how important it is to have current backups.

Disadvantages of an incremental backup

While incremental backups give much greater flexibility and granularity (time between backups), they have a reputation for taking longer to restore because the backup has to be reconstituted from the last full backup and all the incremental backups since. Acronis Cyber Protect Home Office uses special snapshot technology to rebuild the full image quickly for restoration. This makes incremental backups much more practical for the average enterprise.

Generally, incremental and differential backups work towards faster backups and optimized storage space compared to full backups. They are both a form of cumulative backup, quicker than a full backup, but that doesn't mean they are the same.

Let's go over the incremental versus differential backup debate more in depth below.

The backup speed

Regarding backup time (and hence, backup speed), a full backup is slower than both differential and incremental backup. Incremental backup is the fastest, with differential backup coming in second. However, there are exceptions to the status quo here.

If, for example, you have added or changed files containing more data than the files in the initial full backup, then incremental and differential backups will take more time than the full backup. Incremental and differential backups take a similar time to complete if you add only a few new files and don't delete any from the original backup. Nonetheless, incremental backups are considered quicker than differential backups in all other cases.

Storage space use

In general, differential backups require more storage space compared to incremental ones. This is due to storing more significant data volumes in the form of image files - which, in turn, requires more space for the image files. Additionally, the difference grows if your backup schedule is longer (a longer schedule means more extensive data volumes to store as image files, hence — more space taken in storage).

Cost difference

The cost comparison of backup strategies is measured primarily by the storage space taken for each backup type. As we've discussed, full backups would be the most costly, as they require the most storage space. Then come differential backups, with incremental backups being the most cost efficient.

However, this is true in a general, short-term example. Suppose your backup operation spans months or years — the incremental backup approach will take up more space than the initial full backup (as subsequent incremental backups will pile up; unless you audit said backups, you may have storage space issues in the future).

Data restoration speed

Data recovery requires at least one full backup. Additionally, you'd need the most recent differential backup copy to perform a differential recovery and every incremental backup completed since the previous full backup up until the point of recovery to perform an incremental recovery.

With that in mind, differential backup recovery requires fewer steps than incremental recovery, so it will take less time. Restoring from an incremental backup is more time consuming because it depends on multiple backup copies being restored. If any of the previous incremental copies (since the last backup) are missing or corrupted, the recovery time may increase. Additionally, you may experience an incomplete data recovery or a failed recovery altogether. Nonetheless, incremental backup recovery is the preferred choice if you only need partial restoration of recently added data.

Cloud backup benefits

As we've discussed, incremental data copies consume fewer resources. That makes them better suited for the cloud. As they typically take less storage space, this translates into lower cloud storage costs.

When would you use a differential backup?

Firstly, both differential and incremental backups require at least one full backup copy in storage. That said, differential backups work better for companies that can afford more extensive storage, as differential backups typically take up more storage space. However, they require less recovery time, so organizations reliant on minimum downtime will benefit more from them.

Even if the first partial backup performed after the original full backup will be the same, the following instances may differ significantly, depending on the chosen backup method. As differential backup will always back up the data that has changed since the last full backup, differential copies will become larger. Nonetheless, their recovery will take less time than an incremental backup recovery, so your business will experience less downtime if a disaster or a hacking attack occurs.

When would you use an incremental backup?

As we've said, incremental backup is often quicker and takes up less space in storage. Businesses that wish to optimize storage space and don't add vast volumes of changed data to storage since the last backup will benefit more from incremental backups. However, in a disaster recovery scenario, incremental backup recovery will take more time than differential backup recovery. This can translate to more downtime and slower business process resumption.

Incremental versus differential backup: Which is faster?

The incremental versus differential debate is different depending on your specific business and company structure. Data backup strategies are crucial for every organization handling critical information, so all the data in your control must undergo dedicated planning.

In general, differential backups take more time than incremental ones to complete. However, when it comes to recovering backup files, the tides change — differential restores are faster than incremental ones, as you need fewer data pieces to complete the recovery process.

Depending on how much data you need to back up, your network speed, and choice of storage (local, cloud or hybrid), your company must find the optimal smart backup scheme.

Acronis Cyber Protect Home Office provides a unique integration of reliable backup and cutting-edge anti-malware technologies that safeguard data against all of today's threats — disk failure, accidental deletion, and loss and theft, as well as cybercriminal attacks. PCMag described it as "an all-encompassing tragedy prevention solution" in their "Editor's Choice" review.

With Acronis Cyber Protect Home Office, individuals and small businesses can back up their data — including operating systems, applications, settings, files and Microsoft 365 accounts to local drives, external hard drives, NAS and the Acronis cloud. In addition, Acronis Cyber Protect Home Office stops cyberattacks — including attacks resulting from zero-day vulnerabilities — from harming both backup and device data with real-time protection, vulnerability assessment, on-demand antivirus scans, web-filtering, ransomware protection, and a cryptomining blocker. In case of a disaster, data can be easily recovered.