When you configure a backup job, there are typically three types of backup available for your setup: full backup, incremental backup, and differential backup... but what’s the difference?
It's important to understand the difference between these three types of backups and how they works to properly configure your backup strategy.
Types of backup
During the design of your backup strategy, it's crucial to establish how data should be backed up and what method best fits into your business.
Full backup
A full backup includes all data of the selected objects (VMs, physical machines) configured in the Backup Job. A full backup is typically quite large and requires lots of space in the backup repository.
Unless you have an extremely high storage capacity, performing a daily full backup is not recommended mainly for three reasons:
- It consumes resources from the production infrastructure affecting the overall performance.
- It consumes a lot of storage space.
- It takes long time to complete due to the amount of data to backup.
Typically the full backup is performed once a week or more depending on the configured retention in the Backup Job.
Modern software solutions such as Vembu BDRSuite provide the capability to create the appropriate Backup Job to meet the business requirements.
Incremental backup
When you configure an incremental backup type, the first backup is always full while all subsequent backups will backup only data that has changed since the previous backup.
To better understand how an incremental backup works, let's suppose you configured an incremental backup type with a seven days retention. The working concept is pretty simple:
- You have a full backup let's say on Sunday.
- Because the incremental configuration, the incremental backup on Monday will include only the data that has changed from the full backup run on Sunday.
- Tuesday the incremental backup will include only the data that has changed since Monday.
- The process repeats until the next full backup.
In a VMware vSphere environment, the incremental backup process leverages the CBT technology that allows to backup only changed blocks since the previous backup. This makes the backup process faster saving lot of time and optimizing the storage usage.
There are two types of backups you can configure when using incremental:
- Forward incremental
- Reverse incremental
Forward incremental
After the full backup has been taken, subsequent backups will backup only data that has changed since the previous backup.
- Pro - Forward incremental backup is very fast and consumes less space in the repository compared to full or differential backup.
- Cons - Because the full backup is located at the beginning of the backup chain, the restore process will take longer time to complete. An additional amount of space is also required during the transformation process when the retention expires and a new full backup is created.
Reverse incremental
Similar to the forward incremental, after the full backup has been taken, subsequent backups will backup only data that has changed since the previous backup.
- Pro - Less space is required during the transformation process (when the new full is created when the retention expires) and the restore process is faster because the full stays always at the end of the backup chain.
- Cons - Reverse incremental backup is slower than forward incremental since the process has to inject each time the incremental into the full moving the full at the beginning of the backup chain.
When you configure a Backup Job, you need to specify the types of backup to use.
Differential backup
Compared to the incremental backup type, the differential backup will include only data that has changed since the last full backup.
Also a differential backup always begins with a full backup. Once the full backup has been completed, only data that has changed since the full backup is included in the new differential backup.
- Plus - Differential backups are faster than full backups because they have a minor amount of data to process and the restore process is faster than incremental since there are few restore points to process.
- Cons - The amount of backed up data grows with each backup until next full backup.
Modern software replaced the differential backup with thte Reverse incremental since there is a better space optimization and performance.
What method should be used?
Type of backup to use for your backup strategy always depends on business requirements and available software/hardware. For example, it makes no sense to implement a differential backup if you have a poor storage device with low capacity.
The incremental backup is generally the most used option because it's faster compared to other types of backups, consumes less space and allows to take more than one backup per day especially for mission-critical machines.
If the business requires a fast restore (RTO) instead, you should evaluate if the reverse incremental or differential backup is the solution that you need.
Modern software solutions support all types of backups and can achieve good performance in terms of speed and space optimization although the available backup infrastructure (bandwidth, storage device, networking, used software, etc.) makes the difference.
