Synology Incremental Backup: How It Works

Synology incremental backup is a built-in feature of Hyper Backup that only copies data changed since the last backup, saving storage space and time. You enable it by choosing a backup destination and schedule, and Synology automatically handles the rest, creating restore points you can browse by time. This article explains how incremental backup works on Synology NAS, how to set it up, and how to choose the right settings for your data.

What Is Incremental Backup on Synology?

Incremental backup means that after the first full backup, each subsequent backup only stores the blocks that changed. Synology’s Hyper Backup uses this approach by default for most destinations, including external drives, another Synology NAS, rsync servers, and cloud storage like S3 or Azure. The first backup is always a full copy; afterwards, only new or modified data is transferred.

This is different from a differential backup, which copies all changes since the last full backup. Incremental backups are faster and smaller but require all previous increments to restore to a specific point. Synology handles this transparently – you just pick a date and time in the restore wizard, and it reconstructs the files from the full backup plus the relevant increments.

How to Set Up Incremental Backup in Hyper Backup

Setting up an incremental backup takes a few minutes in DSM (DiskStation Manager).

1. Open Hyper Backup from the DSM main menu.
2. Click + and choose Data backup task.
3. Select a destination: local shared folder, external USB drive, remote NAS, rsync server, or cloud service.
4. Choose the folders and applications you want to back up.
5. Set a schedule (e.g., daily at 2:00 AM).
6. Enable Enable backup rotation and pick a retention policy (by number of versions, by time, or both).
7. Finish the wizard – the first backup runs immediately or on schedule.

Hyper Backup automatically performs incremental backups after the first full one. You don’t need to select “incremental mode” anywhere; it is the default behavior.

Retention Policies and Versioning

Retention determines how many incremental versions you keep. Synology offers three main policies:

• By number of versions – keep the latest N backups, delete older ones.
• By time – keep versions from the last N days, weeks, months, or years.
• Custom – combine both, e.g., keep hourly versions for 24 hours, daily for 7 days, weekly for 4 weeks.

Be careful: older versions are permanently deleted when they expire. If you need to keep a specific state forever, create a separate backup task or use Synology’s Snapshot Replication for shared folders, which works differently (block-level snapshots, not file-level backups).

Common Problems and Misconceptions

One common misconception is that incremental backups are less safe because they depend on the chain of increments. If one increment is corrupted, later restore points may fail. In practice, Hyper Backup stores each version as a set of blocks and can often restore from the last good increment, but a damaged block in the middle can break the chain. To mitigate this, Synology allows you to run an integrity check on the backup repository, and you can also enable encryption and checksums.

Another issue: if the backup destination runs out of space, the task fails and you may lose the ability to create new increments. Monitor storage usage and set up alerts in DSM.

Some users confuse incremental backup with versioning in SMB shared folders. Hyper Backup creates its own repository format; you cannot browse it directly as files on the destination. To restore, you must use Hyper Backup’s restore wizard.

Incremental vs. Full vs. Differential

Here’s a quick comparison:

• Full backup – copies everything every time. Simplest to restore but slow and storage-hungry.
• Incremental – copies only changes since the last backup (full or incremental). Fast and small, but restore requires replaying all increments.
• Differential – copies changes since the last full backup. Restore needs only the full plus one differential, but each differential grows over time.

Synology Hyper Backup only offers full + incremental, not differential. If you need differential, you would have to use rsync scripts or third-party tools.

Costs and Storage Considerations

Incremental backup reduces storage usage, but the first full backup can be large. For cloud destinations, you pay for storage and possibly egress when downloading. Synology does not charge for the feature itself; it is included in DSM. However, if you back up to a public cloud, you pay the cloud provider’s fees. To estimate storage, multiply the size of the full backup by roughly the number of versions you keep, assuming changes are small.

Safety and Best Practices

Incremental backup is not a substitute for a disaster recovery plan. Follow these practices:

• Keep at least one backup offsite (cloud or remote NAS).
• Test restores regularly – a backup you can’t restore is worthless.
• Enable encryption for sensitive data, but store the encryption key securely – losing it makes the backup unrecoverable.
• Use a UPS for your NAS to avoid corruption during power outages.
• Set up email or push notifications for backup failures.

Hyper Backup also supports backup integrity checks on a schedule – enable them to catch corruption early.

Frequently Asked Questions

Does Synology Hyper Backup do incremental backups automatically?

Yes. After the first full backup, every scheduled backup is incremental by default. You don’t need to configure anything special; just set the schedule and retention.

Can I restore a single file from an incremental backup?

Yes. In Hyper Backup, choose Restore, select the version you want, and browse to the file. It will reconstruct the file from the full backup plus all necessary increments.

How much storage do I need for incremental backups?

It depends on your change rate. If you modify 1% of 1 TB daily, each increment is ~10 GB. Over 30 days, that’s 300 GB plus the initial 1 TB full backup.

Can I back up to an external USB drive with incremental?

Yes. Hyper Backup supports local and external drives. The drive must be formatted with a filesystem DSM can write to (ext4, Btrfs, exFAT, etc.). Note that the backup repository is not directly readable – you must use Hyper Backup to restore.

What happens if an incremental backup fails?

The task stops and marks the failure. The next scheduled backup will try again, but if the failure is due to a corrupted repository, you may need to create a new backup task. Always check the log and run an integrity check.

Is incremental backup safe for long-term archiving?

Not ideal. For long-term archives, consider making a full backup periodically and storing it separately. Incremental chains become fragile over years, and a single corrupted block can affect many versions.

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