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

Differential and incremental backups are advanced backup strategies that can optimize backup time and storage space by only backing up changed files. However, the data backup process differs significantly for both approaches, as do the resulting backup files. Organizations must understand these differences to design a unique backup plan to reduce backup time, downtime, and storage space costs.

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

1. Full backups comprise entire data backup sets, regardless of already existing backups or data change circumstances.
2. Differential backups comprise data files that have changed since the most recently completed full backup.
3. Incremental backups comprise data files that have changed since the most recently completed full or incremental backup.

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

Typically, full backups are only done on a weekly or monthly basis and are part of a comprehensive backup plan. The relatively long intervals between full backups mean much data will be lost if something goes wrong. That's why it's imperative to back up data between full backups.

Only a tiny percentage of the information in a partition or disk changes daily or even weekly. For that reason, daily backups should only include said changed information. This is where the incremental and differential backup types come into play.

With Acronis True Image, you can create a full backup of your system, which includes the operating system, applications, and data. (either in a browsable form or as a backup image file)

Incremental backups back up only the changed data since the last backup activity — a full or incremental backup.

The incremental backup process requires one full backup followed by subsequent incremental backups over time. Let's look at an example:

Note: Upon completing the latest full backup, the incremental backups will "reset", use the new full backup as a starting point and continue to backup daily until the next full backup.

As described in the example, most companies will execute full backups over the weekend. This is done because the initial full backup takes more time to complete; creating it during off-work hours is sensible as your business is less likely to require the backed-up data.

Suppose you must restore data from the incremental backup sets (to ensure an up-to-date or full backup recovery). In that case, you must apply all incremental backups performed since the last full backup to that initial full backup.

Incremental restores may take an extended time to effectively reconstruct a new full backup, but the overall backup and recovery time would still be faster than creating daily full backups. Moreover, it will optimize storage space and may negate additional storage expenditure.

Companies can create various types of incremental backups to satisfy different data updating and recovery scenarios. Below, we explore the most common approaches.

As discussed, regular incremental backups copy only the files that have changed since the last backup activity. They are typically used when the target data amount is too voluminous to do daily full backups.

Back in the day, backup administrators would use the time between the end of the current workday and the start of the next as a backup window to complete all necessary backups. However, modern organizations handle more extensive data volumes and operate round-the-clock, effectively " erasing" the backup window.

Instead of reading and copying data from primary storage, the synthetic backup method uses (reads) the last full backup and subsequent incremental backups to create a synthetic full backup. Companies can leverage this methodology to avoid creating traditional full backups and thus minimize the impact on network performance and day-to-day processes.

Incremental forever backup (or "progressive incremental backup") is similar to synthetic full backup. It requires only a single full backup to initiate the backup process. Then, subsequent backups (incremental) are created indefinitely and transferred to a centralized backup platform. When you need to restore a data backup, the backup system generates a full backup on the fly and transfers it to the backup client.

This process is made possible by sending each of the incremental backups to disk (physical) or cloud storage. In Incremental Forever, the backup system breaks backup data into chunks and saves them to the preferred backup destination. It also stores metadata about each backup chunk in a persistent system to create point-in-time backups that map to each data chunk comprised in the incremental forever backup. This enables the backup system to easily apply incremental changes to the disk- or cloud-based full backup copy.

Reverse incremental backup is similar to a synthetic full backup. As with all other incremental approaches, this one also requires companies to initially create at least one full backup. When backup admins create the first incremental, it is applied to the original full backup to form a new full backup copy without altering the initial full backup.

The next incremental backup is created by comparing and capturing changed data against the new full backup; it then uses the changed data to form another, up-to-date full backup. This approach ensures you will always have a readily available full backup without having to apply each incremental to the first full backup copy. Moreover, you can revert to any earlier full backup copies when needed to counter advanced system compromise.

Forever Forward incremental backups rely on creating a single full backup, followed by subsequent incremental backups. This backup method only retains one backup generation in the backup server.

Here, the backup system regularly renews the full backup copy by merging the latest relevant increments. Once the new full backup is compiled, the previous full and incremental backup copies are deleted according to a set retention policy to optimize storage space usage.

A multilevel incremental backup is among the more sophisticated backup strategies regarding partial backups; it leverages multiple numbered backup levels to create a backup chain.

• The full backup is marked as "level 0".
• • A "level N" backup includes and backs up all data that has changed since the last “level N-1” backup
  

For example, you create the first full backup on a Sunday via the multilevel approach. This is your starting point, or "level 0". On Monday, you take an incremental backup, automatically labeled as a "level 1" backup. The Level 1 backup will only include data that has changed since the Level 0 backup. (in other words, it will only back up changed and new data since Sunday)

On Tuesday, you will create another incremental backup, labeled "level 2" backup, and only include changes made to your data since Monday. On Wednesday, you will create the next incremental backup, labeled "level 3", and so on.

If you create the Level 2 backup on, let's say, Friday, it will include all data that has changed since Monday. (as the most recent N-1 level backup - Level 1 - was taken on Monday)

In block-level incremental backups, the backup software comprises and backs up storage blocks written with new or modified data instead of backing up entire files and folders.

Block-level backups can be more efficient than file-level backups as they only back up changed blocks of data instead of backing up the entire file. Moreover, some storage systems, such as storage area networks (SAN), access data on the block level, meaning this approach can yield faster backup speed in specific scenarios.

The last common approach is even more granular than block-level backups. Byte-level incremental backup perceives the file system as individual bytes and only backs up bytes that have changed since the last backup process. Since so much less data is comprised in a byte-level copy, it can yield the smallest available backups.

A differential backup backs up only the files that changed since the last full backup rather than the last differential backup.

Note: Differential backups take less backup time than full backups because so much less data is backed up. However, the amount of data being backed up grows with each differential backup until the next full backup

The differential backup strategy (sometimes referred to as "differential incremental backups") requires one full backup to use as a comparison for subsequent backups. Once the full backup is completed, differential backups use it to identify new or modified data to back up. As more and more data is created or changed since the last full backup, it is flagged as available for a differential backup. Companies can determine the differential backup schedule to initiate the process and continuously copy and transfer cumulative backup data to storage.

If you need to restore data in a disaster recovery scenario, you only need the last full backup and the latest differential backup. However, regular differential data backups take more space than cumulative incremental backups, so organizations must set sensible backup retention policies to avoid storage space issues.

Generally, both incremental and differential backup approaches work towards faster backups and optimized disk 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 explore the incremental vs. differential backup debate more deeply below.

Regarding backup time (and hence, backup speed), a full backup is slower than a 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.

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

The cost comparison of backup strategies is measured primarily by the storage space required for each backup type. As we've discussed, full backups would be the costliest since they need more storage space. A differential backup strategy comes in second, 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 in the backup server; unless you audit said backups, you may have storage space issues in the future). Cumulative differential backups will take even more storage space than the initial full backup, making backup audits mandatory to optimize storage costs.

Data recovery requires at least one full backup. Additionally, you'd need the most recent differential backup copy to perform a differential recovery and all subsequent incremental backups completed since the previous full backup up until the recovery point 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 restoring multiple backup copies.

The recovery time may increase if any of the previous incremental backup copies (since the last backup) are missing or corrupted. Additionally, you may experience an incomplete data recovery or a failed recovery altogether. Nonetheless, incremental backup recovery is preferred if you only need partial restoration of recently added data.

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

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.

As we've said, incremental backup is often quicker and takes up less storage space. Businesses that wish to optimize storage space and don't add vast volumes of changed data to backup storage will benefit more from incremental backups.

However, in a disaster scenario, incremental backup recovery takes longer than differential backup recovery. This can translate to extensive downtime and slower business process resumption.

The incremental vs. differential debate can differ depending on your 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 require more time than incremental ones to complete. However, when 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 your choice of storage (local, cloud, or hybrid), your company must find the optimal smart backup scheme. You can also answer the following questions to help you design a unique backup strategy to suit your specific business and industry:

Reliable, regular data backup is critical for organizations across various industries. However, there's no "one-size-fits-all" backup approach. Businesses must take the time to create a unique backup process suited to their specific requirements.

Some companies may rely only on full backups, while others implement full, incremental, and differential backups to safeguard all the data on their network. Combining all backup types can be challenging, especially if you rely on multiple solutions to create reliable backup sets. Moreover, dedicated backup software is often too expensive or requires extensive expertise to pilot. On the other hand, Acronis Cyber Protect offers SMBs and enterprises an affordable, easy-to-use centralized solution to reduce backup speed, ensure top-tier data protection, and minimize downtime via efficient disaster recovery.

With Acronis Cyber Protect, you can create full, incremental, and differential backups to support sophisticated backup strategies from a single platform. Moreover, you can monitor and manage the backup process via a user-friendly interface without a dedicated on-premises IT team. You can customize your preferred backup schedule to ensure regular backups without disrupting normal business operations.

Once those backups are created, Acronis Cyber Protect will safeguard them via hybrid protection, including AES-256 encryption (for data at rest and in transit), storing multiple backup copies in different locations (local, off-premises, the Acronis cloud), and advanced cybersecurity features powered by AI and machine learning. This will ensure that all backup files are readily available for access and rapid recovery to minimize downtime and ensure business continuity regardless of the disaster-recovery scenario.

Acronis Cyber Protect is also designed to enable optimal scalability to serve businesses of various sizes. Whether you house a single server or a complex server infrastructure, the backup software can scale to accommodate your specific requirements.