Backups are an essential part of your operations because data is invaluable, and you don’t want to lose it due to a software/system crash, faulty hardware, or other reasons. But these backups are not easy given the explosive jump in data volume and the cost of storage devices, which is why there are many backup strategies that help you optimize data storage without spending a lot of money. Two such popular backup strategies are incremental and differential backup. In this article, we’ll explore what each means, its advantages and disadvantages, and which is a good strategy in a given situation.
In a differential backup, all the changes that were done since the last full backup will be copied. The full backup is the master copy, and each time, the backup process will check the existing data with the full backup and update the changed data. In many ways, differential backup was seen as an evolution in the world of backup as it gave companies a way to avoid the expensive and time-consuming process of doing a full backup each time.
How does it work? Let’s see an example. Let’s say you did a full backup on Sunday. On Monday, you check the files against the Sunday backup and upload the changed ones. On Tuesday, you check the files against the Sunday backup and upload the changed ones, and so on. As you can see from the example, you compare the changes against the full backup only.
- The latest differential backup and the full backup is enough to restore data.
- More flexible to implement than a full backup.
- Reduced chance of data loss as you can always check with the previous version.
- This backup strategy can take up storage space as the data is compared against the full backup, and hence, the number of changes will keep increasing by the day.
- Not ideal for organizations that have long intervals between full backups.
- It is time-consuming, especially if a full backup is not done often, as the backup process checks with the last full backup, identifies the changed content, and uploads it all.
As the name suggests, in an incremental backup strategy, you only back up those files that have changed since the last backup. This means the incremental or modified data alone is backed up every time.
For example, you did a full backup on Sunday, and on Monday, you check the files against the Sunday backup and upload the changed ones. On Tuesday, you check the files against the Monday backup and upload the changed ones, and so on.
As you can see, you compare the existing data with the last incremental backup and upload the changed content. So, the last backed up data is the benchmark for comparison. Needless to say, this strategy comes with many pros and cons.
- Only the changed content is copied each time, so the backup window is short.
- Ideal if you’re dealing with sensitive data and want backups to run every hour.
- During the data restoration process, the full backup and all the incremental copies have to be restored, which can be time-consuming.
- An increased chance for data loss due to corrupted or lost disks because data of a particular version is not available in any other backed-up files.
Incremental vs. differential backup
Both backup strategies are based on the principle that not all data changes between backups, so it makes sense to upload only the changed data instead of a complete or full backup each time. Undoubtedly, this saves time and storage.
The key difference between the two strategies is the way the changes are identified. In differential backup, the existing data is compared each time with the last full backup, and the difference is uploaded. On the other hand, in incremental data, the existing data is compared with the last incremental backup and not the last full backup, and the changed data is uploaded.
A key aspect from an implementation standpoint is the archive bit. When you do a full backup, it resets the archive bit.
Likewise, an incremental backup will also reset the archive bit every time, so only the changes are copied, but a differential backup will not reset the archive bit, so all the data differences between the full backup and the current data are copied.
These differences are summarized in the table below.
|Compared with the last incremental backup.||Compared with the last full backup.|
|Quick as it compares with the last incremental backup.||Slower as it has to compare with the last full backup and identify all the changes.|
|Requires lesser bandwidth to upload since the changed data will be relatively less.||Requires more bandwidth than incremental backup as the comparison is made with full backup data each time.|
|Restoring data requires the full data backup and every incremental copy.||Restoring data requires only the full backup and the last differential copy.|
|Restoration is slower, as all copies have to be reconciled.||Restoration is quicker as only the latest copy has to be reconciled.|
|Resets the archive bit.||Doesn't reset the archive bit.|
|Increased possibility of data loss.||A relatively lesser chance for data loss.|
Which is better?
Now comes the big question — which is better? Incremental or differential backup?
Well, it depends on your backup strategy, frequency of backup, the possibility of data changes, the terms of your service level agreements, available resources, and frequency of restoration.
Choose incremental backup if:
- The time period between full backups is long.
- You’re running short of storage space.
- You want short backup windows.
- You’re handling sensitive data and want backups to run every hour.
On the other hand, choose differential backup if:
- Storage space is not an issue.
- Backups happen overnight and don’t impede any other process.
- The time between full backups is less.
- Quick data restoration is a key business requirement.
Thus, both incremental and differential data backups come with their own unique advantages and disadvantages, so the right backup strategy depends on your needs.
Which of the two do you prefer and why? Please share your experience with our readers in the comments section.
Featured image: Shutterstock