DSM 7.4 Storage Efficiency: Real HDD Savings So Far

Synology

When Synology launched DSM 7.4 in June 2026, one of its most interesting storage features was easy to summarize: HDD volumes could finally use post-processing deduplication and compression to reduce the amount of physical storage consumed by files. Synology reported HDD data-reduction ratios as high as 3.5:1. A few months later, the more useful question is no longer whether the feature exists.

It is:

How much space does it actually save on a real NAS?

The answer depends heavily on what you store.

Office documents, archives, duplicated project folders, logs, and repeated business files can be strong candidates. Large collections of already compressed video, photographs, music, and other unique files may show dramatically smaller gains.

What DSM 7.4 Actually Does on HDD Volumes

DSM 7.4 introduced two data-reduction technologies for supported HDD-based Btrfs volumes:

Data deduplication identifies duplicate data so the NAS does not need to retain redundant copies of the same information.

Compression reduces the physical storage required for data that can be efficiently compressed.

On HDD volumes, Synology applies these features at the shared-folder level rather than automatically processing the entire volume.

That distinction has proven useful.

Administrators can target folders that are likely to benefit instead of making every workload participate in background data reduction.

For example:

Projects → enable

Document Archive → enable

Logs → enable

Historical Files → enable

Video Library → probably analyze first

Surveillance Recordings → probably leave alone

Selective deployment is generally more useful than enabling the feature everywhere simply because DSM offers it.

The 3.5:1 Number Is Not a Promise

Synology reports HDD data-reduction ratios between 1.5:1 and 3.5:1 across its real-world internal file-storage workloads, including file collaboration, log retention, and document archiving. That is an important range rather than a guaranteed result. A 3.5:1 reduction means approximately 3.5 TB of logical data could occupy around 1 TB physically under highly favourable conditions. But that does not mean your 20 TB NAS suddenly becomes equivalent to 70 TB of physical storage.

Real-world savings depend on:

Duplicate content
File types
Compressibility
Dataset age
User behavior
Snapshot configuration
Shared-folder selection
Workload characteristics

The less redundancy and compressibility your data contains, the less impressive the result becomes.

Early Real-World Results Show Just How Wide the Range Can Be

Community testing since DSM 7.4 arrived illustrates this clearly.

One user testing a DS925+ reported an NVMe volume saving approximately 18.7 GB from 44.3 GB after deliberately adding duplicate movie files. On the same NAS, a Synology HDD volume reportedly saved only about 160 MB from 16.1 GB when Storage Efficiency was enabled on selected music, photo, and video folders. Another community example reported that analysis of a mixed dataset exceeding 20 TB predicted less than 1 GB of savings. A separate DS925+ test reportedly estimated only about 7 GB of savings from 1 TB of data, leading the user to decide that enabling the feature was not worthwhile for that workload.

These are individual community reports, not controlled benchmarks, but collectively they illustrate the most important lesson:

Your dataset matters more than the headline reduction ratio.

Media Libraries Often Have Less to Give

A Plex or Jellyfin library may contain enormous amounts of data while being a poor candidate for Storage Efficiency.

Video files are already highly compressed.

The same applies to formats such as:

JPEG
HEIC
MP3
AAC
H.264
H.265/HEVC
AV1
ZIP archives
Other compressed media

Compression cannot magically extract huge additional savings from data that has already been efficiently compressed.

Deduplication can still help if identical files actually exist in multiple locations, but a library containing thousands of unique movies or photographs may offer relatively little duplicate data.

This explains why a NAS with 30 TB of media can potentially save less space than a much smaller business file server containing heavily duplicated documents.

Business File Shares Can Be Much Better Candidates

Now consider a shared business volume.

Employees frequently create:

Project Copy

Project Copy Final

Project Copy Final 2

2025 Project Archive

2026 Project Archive

Several departments may also maintain their own copies of:

Templates
Presentations
PDFs
Reports
Documentation
Project deliverables
Exported datasets
Historical folders

That environment creates far more opportunity for deduplication.

Document-oriented data may also compress more effectively than already compressed media.

This is why DSM 7.4 Storage Efficiency can have considerably greater financial value in business file collaboration and document archival environments than on a home media server.

Cold Data Is Where Synology Says to Use It

Synology’s current Storage Efficiency documentation specifically describes HDD deduplication and compression as best suited for cold data and archival workloads.

That is an important operational recommendation.

Storage Efficiency should not automatically be applied to the busiest shared folder simply because it occupies the most capacity.

A better candidate may be a large archive that:

Grows steadily
Contains historical data
Includes repeated files
Changes infrequently
Is rarely performance-sensitive
Consumes significant HDD capacity

In other words, target expensive capacity problems where the performance sensitivity is low.

Use the Analysis Before Turning It On Everywhere

The practical lesson from early DSM 7.4 deployments is simple:

Estimate the potential benefit before committing to the workload.

If analysis suggests that a 10 TB shared folder will recover only a few gigabytes, there may be little operational reason to process it. If another folder containing project archives shows substantial reduction potential, that is a much stronger candidate. Storage Efficiency should be treated like any infrastructure optimization.

Measure first.

Optimize second.

Scheduling Matters on HDDs

Data reduction is a background storage operation. That matters much more on mechanical HDDs than on high-performance SSD storage.

HDDs have limited random I/O capability, and the same disks may already be servicing:

SMB users
Synology Drive
Backups
Snapshots
Media applications
Databases
Containers
Virtual machines

Adding data-reduction processing during the busiest part of the workday can create unnecessary contention.

Synology therefore provides scheduling controls for Storage Efficiency tasks.

Use them.

Run Storage Efficiency During Quiet Periods

For a normal office NAS, a sensible schedule might be:

Start: Midnight

Stop: 6:00 or 7:00 AM

That gives DSM a recurring maintenance window without forcing the NAS to compete heavily with employees during normal business hours.

A 24/7 business may need a different approach.

Look at actual workload patterns in Resource Monitor and identify periods when storage I/O is lowest.

The correct maintenance window is based on your NAS usage, not an arbitrary time copied from someone else’s configuration.

Don’t Stack Every Maintenance Job Into the Same Window

This is an easy mistake.

An administrator schedules:

Hyper Backup at midnight
Data scrubbing at midnight
Storage Efficiency at midnight
Antivirus at midnight
Snapshot maintenance at midnight

Then wonders why the NAS sounds like it is rebuilding itself every night.

Spread heavy background operations across different maintenance windows where practical.

For example:

Night 1: Backup

Night 2: Storage Efficiency

Weekend: Data scrubbing

The exact schedule depends on business requirements, but the principle is to avoid unnecessary I/O competition.

Performance Impact Is Mostly About When Processing Happens

Early community discussion has included concerns that HDD deduplication could severely reduce performance. That concern needs context. The most obvious impact occurs while Storage Efficiency is actively analysing and processing data because the HDDs must perform additional work. That does not mean enabling the feature automatically makes normal file access permanently slow.

Synology specifically designed HDD Storage Efficiency as a post-processing system and provides scheduling controls so data reduction can occur outside performance-sensitive periods. For lightly accessed archives, the operational impact may therefore be almost invisible to users if the maintenance schedule is designed correctly. For heavily active data, the calculation is different.

Snapshots Can Reduce Your Savings

This is one of the most important details to understand before judging Storage Efficiency results. Synology states that Storage Efficiency tasks cannot process data that is referenced by a snapshot. That means Snapshot Replication and aggressive snapshot retention can limit the amount of data available for deduplication or compression. This creates an interesting trade-off.

Snapshots provide valuable:

Point-in-time recovery
Ransomware protection
Accidental deletion recovery
Replication capabilities

Storage Efficiency provides:

Capacity reduction

Do not weaken a good recovery strategy simply to produce a more impressive deduplication number.

Instead, review whether your snapshot retention policy is sensible.

Keeping hundreds of unnecessary historical snapshots may consume storage and reduce optimization opportunities. But removing recovery points that the business genuinely needs just to improve a storage-efficiency ratio is the wrong priority.

Coordinate Snapshot and Storage Efficiency Schedules

Synology specifically provides guidance for using Snapshot Replication alongside Storage Efficiency. The schedules should be planned together. If snapshots constantly reference data before Storage Efficiency has an opportunity to process it, savings can be reduced. A better workflow may provide a processing window where Storage Efficiency can operate before another snapshot cycle captures newly written data.

The optimal timing depends on:

Snapshot frequency
Retention
Data-change rate
Recovery objectives
Shared-folder activity
Available maintenance windows

This is one area where thoughtful scheduling can improve results without purchasing any additional hardware.

Don’t Expect Storage Efficiency to Replace Capacity Planning

Suppose DSM reports that you saved 2 TB. That is excellent. It does not mean the business should immediately fill the recovered 2 TB and continue operating the volume near maximum capacity.

NAS systems still need operational headroom for:

File-system activity
Snapshots
Rebuilds
Storage maintenance
Temporary data
Application growth
Future backups

Data reduction should extend the useful life of storage, not encourage administrators to operate permanently at the edge of capacity.

The Real Financial Benefit May Be Delaying Expansion

The most valuable result from Storage Efficiency may not be the percentage shown in Storage Manager. It may be time. Imagine a business NAS gaining 3 TB of effective free capacity. If data is growing at 1 TB per year, that optimization could potentially postpone a storage expansion by several years.

That could delay:

New HDD purchases
Expansion-unit purchases
NAS replacement
Data migration
Downtime
Administrative labor

Viewed this way, even a reduction ratio far below Synology’s 3.5:1 maximum can produce meaningful value.

Storage Efficiency Is Not Equally Available to Every Synology Owner

There is also an important hardware limitation.

DSM 7.4’s HDD data-reduction capability is available only on supported Synology models and requires compatible Synology HDDs under Synology’s official support policy.

It also operates on supported Btrfs volumes.

Community users have demonstrated unofficial methods of enabling Storage Efficiency with some third-party drives, but those configurations are outside Synology’s normal supported design. A community script making the menu option appear does not make the resulting configuration equivalent to an officially validated Synology storage environment. Businesses should consider supportability before building capacity plans around unsupported modifications.

Three Months In, the Best Strategy Is Selective Deployment

DSM 7.4 Storage Efficiency is most useful when administrators stop thinking of it as a volume-wide switch and start treating it as a targeted data-lifecycle tool.

A practical deployment might look like:

Active Projects: Leave alone unless analysis shows meaningful benefit.

Document Archive: Enable.

Historical Project Files: Enable.

Log Archive: Enable.

Video Library: Analyze first; likely limited benefit.

Surveillance Recordings: Prioritize predictable recording performance and retention planning.

Backup Repository: Evaluate carefully based on the backup application’s own deduplication and storage behavior.

That is much more sensible than selecting every shared folder.

What Actually Changed After Real Use?

A few months of DSM 7.4 have made the Storage Efficiency story clearer. The technology can absolutely recover meaningful HDD capacity. But the dramatic headline ratios are workload-dependent.

The strongest candidates are generally cold, repetitive, compressible, document-heavy datasets. The weakest candidates are often unique, already compressed media files and other data with little duplication. Scheduling also matters because post-processing creates additional disk activity, particularly on mechanical drives. Snapshot configuration matters because snapshot-referenced data can limit optimization. And hardware compatibility matters because Synology officially restricts HDD Storage Efficiency to supported models and Synology drives. The biggest lesson is therefore not that DSM 7.4 gives everyone 3.5 times more storage. It is that Synology now gives administrators another way to delay capacity expansion by intelligently reducing the footprint of the right data.

Run the analysis.

Choose the right shared folders.

Schedule processing during low-I/O periods.

Coordinate it with snapshots and other maintenance tasks.

Then measure the savings over several weeks or months.

If the result postpones the purchase of another set of drives or an entire NAS expansion, Storage Efficiency has done exactly what matters—even if your dashboard never comes close to the theoretical maximum reduction ratio.

About Epis Technology

Epis Technology helps businesses optimize Synology storage around real capacity growth rather than headline specifications. Services include DSM 7.4 Storage Efficiency assessments, HDD deduplication and compression planning, Btrfs configuration, snapshot and maintenance scheduling, storage-capacity forecasting, Synology HDD selection, RAID and SHR design, NAS expansion planning, Synology Drive, Hyper Backup, Active Backup for Business, ActiveProtect, and disaster recovery. Epis Technology can analyze existing Synology workloads to determine where data reduction can meaningfully extend storage life and where additional capacity remains the better investment.