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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Choose Duplicati’s block size for the way your files change, remote volume size for the balance between transfer overhead and restore downloads, and retention for the history you need to keep. They control different parts of a backup, so tune them separately. The most important setup constraint is that block size is fixed after the initial backup; changing it means starting a new backup set.
What each setting controls
- Block size splits source files into blocks. It affects how finely Duplicati can identify reusable data when files change, as well as how many blocks it must track.
- Remote volume size controls the size of files Duplicati uploads to the destination. It affects the number of remote files and the amount of data that may need to be downloaded to restore files.
- Retention determines which historical backup versions remain available. Removing old versions and reclaiming the remote storage they occupied are related, but not always immediate, steps.
These are not interchangeable “backup size” controls: block size affects data handling, volume size affects how that data is packaged remotely, and retention governs how much history remains.
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Choose block size for file changes—and decide before the first backup
Smaller blocks can help when files are large and often change in small portions: Duplicati can reuse unchanged blocks and upload changed portions more selectively. The trade-off is more blocks to track, which can add overhead and reduce overall performance. If files are mostly unchanged or tend to change as whole files, smaller blocks may add tracking work without much deduplication benefit.
Duplicati’s backup size parameters guide gives typical block sizes from about 100 KiB for backups under 3 GiB up to 1 MiB. These are contextual recommendations, not benchmarked optima or guarantees; the right choice depends on the size and change pattern of your data.
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Make this choice before running the initial backup. Duplicati says block size cannot be changed afterward because blocks of different sizes cannot be compared. Treat a different block size as a new backup configuration rather than changing an established backup set.
Choose remote volume size for your destination and restore pattern
Larger remote volumes mean fewer destination files and less per-file overhead, such as headers and connection handshakes. The cost shows up during restore: Duplicati must download a full remote volume to restore even a small file, and a restore may involve several volumes.
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| Destination or priority | Documented starting guidance | Trade-off to consider |
|---|---|---|
| Cloud destination | About 50–500 MiB per volume, according to Duplicati’s backup size parameters guide. | Smaller volumes can limit the amount downloaded for a small-file restore; larger ones can reduce file and transfer overhead. |
| Local network | About 500–2000 MiB per volume, according to the same guide. | Larger volumes may suit faster connections, but can increase the amount fetched to restore a small file. |
These ranges are starting points, not provider-specific guarantees. Source size, network speed, destination behavior, and what you restore all matter. Duplicati’s backup setup guide describes its default volume size as a balance for cloud storage and limited network connections, and advises increasing it for fast connections or local networks.
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Documentation also lists a 50 MB default upload volume in its community guide and --dblock-size = 50mb on the advanced-options page. Those pages do not identify a release number. Check the value shown in your installed version rather than assuming a version-specific default; the published default and the wider sizing ranges serve different purposes.
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- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
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Set retention to match the recovery history you need
Choose a policy based on how often backups run and how far back you may need to recover:
- Age-based retention: useful when backups run regularly and you know the time horizon you want to preserve.
- Version-count retention: useful when backups are irregular or triggered by events, so keeping a set number of versions is more predictable than keeping versions by age.
- Bucket-based retention: useful when you want frequent recent recovery points and progressively fewer older ones.
Duplicati’s retention settings documentation gives this Smart retention rule: 1W:1D,4W:1W,12M:1M. It keeps one backup per day over the most recent week, one per week over the next four weeks, and one per month over the last twelve months. The setup guide presents Smart retention as a useful default for most users, but check that its resulting history meets your recovery needs.
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- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop
- To get set up, connect the portable hard drive to a computer for automatic recognition no software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
Duplicati applies configured deletion after a backup and does not delete the last version. Retention can remove old version references without immediately reducing remote bytes: volumes may contain blocks still used by retained versions as well as blocks no longer needed. Reclaiming that space can require compaction, which may download, repack, and upload volumes. Duplicati describes the backup and storage process in How Backup Works.
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A practical setup decision
- Before the first backup, assess file size and change patterns. If large files often change in small portions, consider a smaller block size; if they are mostly unchanged or change wholesale, the tracking cost of smaller blocks may not be worthwhile.
- Choose a remote volume size based on destination and restores. Lean smaller when limiting small-file restore downloads matters; lean larger when reducing remote-file and transfer overhead matters and the connection can handle it.
- Choose retention based on backup regularity and recovery goals. Use age, count, or bucket rules to preserve the history you actually need, then account for possible compaction when estimating storage cleanup.
- Confirm settings in your installed version. Documentation describes general guidance and option defaults, but does not establish one universally best configuration or release-specific defaults for every installation.
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