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Synology software can sometimes reclaim space already occupied by data, but it cannot create new raw storage capacity. The main options are conditional data deduplication and compression, plus careful management of snapshots and retention. If your pool has no free space and you cannot safely reduce or remove data, expansion ultimately requires a supported hardware or storage migration change.
First distinguish reclaimed space from added capacity
“Expand” can mean two different things: reducing how much space existing data occupies, or increasing the pool’s total raw capacity. Free DSM features may help with the first when the data and system configuration are eligible. They do not do the second.
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Synology’s Knowledge Center says pool expansion requires adding drives to the pool or replacing existing drives with larger ones; which changes are supported depends on RAID type and the NAS configuration. See Synology’s expansion guidance before planning a hardware change.
Find what is using space before changing settings
Start by identifying which shared folders, files, backups, or retained versions are consuming capacity. The right remedy depends on what is actually filling the pool: compression is relevant only to data that compresses, deduplication only helps where identical blocks recur, and snapshot retention can affect how much space can be reclaimed.
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Check the documentation for your DSM release and NAS model for the current tools and menu paths. The available information here does not establish a universal DSM storage-analysis path, so do not assume every model or release presents the same controls.
Use storage efficiency only when your system and data qualify
Synology’s Storage Efficiency feature can perform post-process deduplication and compression, but it is not available on every NAS or configuration. Synology documents requirements including a supported Btrfs volume and compatible Synology drives. The feature can also exclude some data types, and processing may affect system performance. Check the Storage Efficiency documentation and confirm eligibility for your model, DSM version, volume, and drives before enabling it.
| Method | When it may help | Important limits |
|---|---|---|
| Deduplication | When identical data blocks recur, such as in some VM images or ISO files. | Requires supported configuration; some data may be excluded. Actual savings depend on the workload. |
| Compression | For data that is readily compressible, such as text, logs, or uncompressed databases. | Already compressed or otherwise unsuitable data may yield little or no reduction; processing can affect performance. |
Synology does not establish a universal savings percentage. Results depend on the content and configuration, so treat any projected reduction as workload-specific rather than guaranteed.
Review snapshots without sacrificing recovery history
Snapshots preserve earlier versions for recovery, but data referenced by snapshots cannot be processed by storage-efficiency tasks. Synology recommends running efficiency tasks before taking snapshots for the greatest reduction; existing snapshots may limit the result. Its snapshot and storage-efficiency guidance, last updated September 30, 2026, says DSM 7.4 and later support deduplication and compression, while DSM 7.0.1–7.3 supports deduplication only.
Do not delete snapshots simply to chase a space estimate. First decide how much recovery history you need, confirm what a snapshot contains, and change retention only if you can accept losing those restore points. Check the current documentation for your DSM release because feature availability can vary by version.
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Use Btrfs quotas and snapshots for management, not extra capacity
Where the model supports Btrfs, its features include snapshots and shared-folder quotas. A quota can set a limit for a folder; it does not enlarge the pool or add usable bytes. Snapshots can help protect data, but their retention has to be balanced against available space.
Filesystem support is model-specific. Synology’s filesystem comparison, last updated December 25, 2023, advises checking the NAS model’s datasheet for supported filesystems.
Do not mistake SSD cache for storage expansion
SSD cache is a performance feature, not extra capacity for files. It requires SSD hardware and is intended for workloads that benefit from caching, such as certain random-I/O patterns. Synology notes that large sequential operations, including HD video streaming, may see limited benefit. See its SSD cache overview and workload guidance.
When software has reached its limit
If storage efficiency is unsupported or does not meaningfully reduce your data, and you cannot safely remove files or shorten retention, software cannot expand the pool’s raw capacity. Synology’s documented expansion routes involve adding drives or replacing drives with larger ones, subject to the RAID type and NAS model. Verify the exact supported path for your system before making changes; Synology also points users to its RAID calculator when assessing drive configurations.
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