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1 July 2024  John Weaver  Senior Program Developer
 

Summary
Incremental backup is a method that saves storage space and reduces bandwidth by only backing up data that has changed since the last backup. Unlike full backups, which copy all data every time, incremental backups start with a full backup and then only capture changes made since the last backup. This approach helps optimize backup routines, making them more efficient and cost-effective.



Table of contents

table iconWhat Is Incremental Backup?
table iconHow Incremental Backup Works
table iconForever Incremental Backup
table iconTypes of Incremental Backup
table iconUsing an Incremental Backup
table iconSummary
Incremental backup is a data backup method designed to reduce storage requirements and bandwidth load while providing the necessary level of data consistency and availability. This article will provide an in-depth overview of this concept, how it works, and how it helps save time and money on backup and disaster recovery routines.

What Is Incremental Backup?

Incremental backup is a type of backup that copies only data that has changed since the previous backup. Unlike a full backup, where the entire data set is copied to the backup storage with every backup job, incremental backup allows you to perform a full backup only once in a while. Each subsequent backup is an increment for the previous backup, hence the name.

How Incremental Backup Works

To illustrate the backup process, let’s assume you have made a full backup and now want to do a weekly backup of any added or changed files:
- Week 1 – first full backup
- Week 2 – added and changed data only since the Week 1 backup
- Week 3 – added and changed data only since the Week 2 backup

Forever Incremental Backup

Forever incremental backup involves performing incremental backups at regular intervals after the initial full backup, eliminating the need for frequent full backups. However, each subsequent backup enlarges the chain of incremental backups, making it more time-consuming and resource-intensive for backup software to analyze the full backup and all increments. Periodical full backups are highly recommended to start a new sequence of incremental backups. The frequency of full backups depends on your business needs—weekly, monthly, or once every couple of months. An advanced technique called a synthetic full backup can simulate full backups.
Backup software vendors typically allow users to set the number of data versions to keep. Incremental backup includes a full backup and a series of subsequent increments. Each subsequent backup (full or incremental) is considered a version. For data consistency, you can’t remove individual elements of this chain, only the entire series from the full backup to the next full backup. Thus, periodic full backups are strongly recommended.
incremental backup view
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  • Version chain mode: Only the latest 5 versions are kept, and useless old versions are automatically deleted after the backup is complete.
  • Single version mode: Only the most recent version is kept, and the previous version is automatically deleted after the backup is complete.
  • Full mode: Create a full backup.
  • Incremental mode: After the initial full backup, only incremental backups are created.
  • Differential mode: After the initial full backup, only differential backups are created.

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Types of Incremental Backup

Different backup types are determined by the size of changes that the software adds to the repository at every subsequent backup. We will overview incremental file-level backup and incremental block-level backup in detail.

Incremental File-Level Backup

In an incremental file-level backup, if a file has been modified, it will be sent to the backup repository to create a new version of it. This backup type is simple to perform and works well for a small data set. However, if the changed files are large, the backup will also be large, extending the duration of the backup job and requiring more storage space.
Incremental backup: File level 

Incremental Block-Level Backup

In a block-level approach, the backup software performs a more in-depth file analysis and copies only the modified portions of files, making it much faster to upload than using a file-level backup.
Incremental backup: block level 

Using an Incremental Backup

Advantages

Compared to the full backup, an incremental type uploads only changed and new files, which allows the reduction of: – Needed storage space – Bandwidth consumption – Computing resources usage Let’s consider different scenarios to back up a 5 GB dataset with a 3% daily change rate for one month and see how effective they are and how much storage space is needed.
- Weekly full backups only: In this case, you will need to set up only 4-5 backups a month, which is quite storage-friendly, especially if your retention policy doesn’t require you to keep several versions of every backup. The main issue here is data reliability. If something malicious happens to your servers or endpoints, you will permanently lose about a week of critical business data. Storage space calculation: 5 * 5 GB = 25 GB
- Full backups daily: When you set full backups every day, it is quite reliable. However, it requires so much storage room, bandwidth, and computing capacity that this backup strategy becomes highly ineffective. Storage space calculation: 22 * 5 GB = 110 GB
- Weekly full backups with incremental backups on weekdays: In this scenario, full backups don’t have to be set very often, and the periods between full backups are covered by incremental sequences. Therefore, this scenario turns out to be the golden mean between saving storage space and providing data reliability. Storage space calculation: (5 * 5 GB) + (22 * 3% * 5 GB) = 28.3 GB
Incremental backups on weekdays and weekly full backups 

Disadvantages

However, this approach has several drawbacks:

- Longer data restore: It takes more time for backup software to find, analyze, and collect the latest full backup and all subsequent incremental backups.

- Less data consistency and reliability: When you need to recover, the backup software analyzes the whole backup chain. If one element in that chain is corrupt, your data is non-recoverable.

Summary

Out of all backup types, the incremental backup is one of the most beneficial backup methods as it assures reliability and accessibility of your data, saves a lot of storage space, consumes less bandwidth, and leads to faster backups compared to a full backup scenario. The flaws such as slower restore and dependence on the increments’ integrity may be addressed by performing the full backup periodically and setting the proper retention policy for your backups.
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