How to Use SSDs and HDDs Together in UGREEN NAS
Use M.2 SSD cache when your HDD storage repeatedly serves the same small files. Create a separate SSD storage pool when applications or active projects need consistently low latency. Keep large media libraries, archives, and backup data on HDDs.
SSD Cache or SSD Storage Pool: Which Fits Your Workload?
SSD cache and an SSD storage pool use the same type of fast storage for different purposes.
Cache keeps frequently accessed copies of HDD data on M.2 SSDs. The original files remain on the HDD volume. A separate SSD pool stores the actual files or application data directly on the SSDs.
| Workload | Recommended layout | Why it fits |
|---|---|---|
| Photo thumbnails and frequently reopened small files | Read-only SSD cache | Repeated reads can produce useful cache hits |
| Many users reading and writing small files | Read-write SSD cache | Accelerates random reads and writes |
| Docker application data, virtual machines, and databases | Separate SSD pool | Provides predictable low latency |
| Active video-editing projects | Separate SSD pool | Large media files benefit more from direct SSD throughput |
| Media streaming and completed video projects | HDD pool | These are primarily sequential workloads |
| Backups and long-term archives | HDD pool | Capacity matters more than SSD latency |
Cache needs repeated access before it becomes useful. The first time you open a file, the system may still read it from the HDD pool. If the file is never opened again, caching it provides no meaningful advantage.
Large sequential transfers are also poor cache candidates. Copying an ISO file, streaming a movie, or moving hundreds of gigabytes of footage usually depends on HDD-array throughput and the network connection. An SSD cache should not be installed solely to make those transfers faster.
Can Your UGREEN NAS Use SSD Cache?
UGOS Pro SSD cache requires:
- A UGREEN NAS with available M.2 NVMe slots
- A volume created on an HDD storage pool
- One compatible M.2 SSD for read-only cache
- Two compatible M.2 SSDs for read-write cache
- An independent backup before changing the storage configuration
The SSD Cache Management option does not appear for an all-SSD storage pool because there is no HDD volume to accelerate.
| UGREEN NAS model | Installed-drive layout | Available SSD/HDD configuration |
|---|---|---|
| DXP2800 and DXP2800 GT | Two SATA bays and two M.2 slots | HDD pool with cache or a separate M.2 SSD pool |
| DXP4800 Plus, DXP4800 Pro, and DXP4800 GT | Four SATA bays and two M.2 slots | HDD pool with cache or a separate M.2 SSD pool |
| DXP6800 Pro and DXP8800 Plus | Six or eight SATA bays and two M.2 slots | Larger HDD array with cache or a separate M.2 SSD pool |
| DXP480T Plus | Four M.2 slots and no SATA bays | All-flash SSD storage; no HDD pool to cache |
| DH2300 and DH4300 Plus | SATA bays without M.2 slots | M.2 cache unavailable; SATA SSDs occupy regular drive bays |
Before buying an SSD, select the exact NAS and SSD model in the UGREEN NAS compatibility list. Matching the M.2 connector or advertised capacity alone does not establish compatibility.
For read-write cache or application storage, also review the SSD’s endurance rating. Workloads that generate frequent writes consume more of the drive’s TBW allowance than ordinary file storage. Our guide to choosing drives for a UGREEN NAS explains TBW, DWPD, sector format, and other drive-selection factors.
If your current NAS lacks M.2 slots and SSD acceleration is essential to the workload, you can browse and filter UGREEN NAS models by drive layout and network speed.
How to Create SSD Cache in UGOS Pro
Shut down the NAS and disconnect its power before installing an M.2 SSD. After installing the compatible SSDs and restarting the NAS, open Storage and confirm that each new drive appears as Unused and Normal.
Choose Read-Only or Read-Write Cache
| Cache mode | SSD requirement | Main consideration |
|---|---|---|
| Read-only | One M.2 SSD minimum | Accelerates repeated reads; an abnormal cache SSD does not remove the original HDD data |
| Read-write | Two M.2 SSDs in RAID 1 | Accelerates small-file reads and writes but introduces delayed-write risk |
Read-only cache is the safer starting point for photo browsing, document libraries, and other workloads dominated by repeated reads.
Read-write cache stores incoming data on the SSDs before synchronizing it to the HDD pool. UGOS Pro therefore requires two M.2 SSDs in RAID 1. A stable power supply is especially important because an interruption can affect data that has not finished writing to the HDDs. Use a compatible UPS and follow our guidance for protecting UGREEN NAS from power outages.
Read-write cache can also cause periodic HDD activity while cached data is written back to the storage pool. If drive hibernation, noise, or minimum idle power is a priority, account for that behavior before enabling it.
Create the Cache
Important: Creating SSD cache formats the selected M.2 SSDs and erases their existing data. UGOS Pro also temporarily disables applications associated with the target volume while the cache is being built.
- Sign in to UGOS Pro with an administrator account.
- Open Storage.
- Select Storage > Storage Pool & Volume.
- Find the HDD storage pool you want to accelerate.
- Open the
···menu and select SSD Cache Management. - Select Create.
- Choose the HDD volume that will use the cache.
- Select Read-only cache or Read-write cache, then select Next.
- If you selected read-write cache, read the delayed-write warning and acknowledge the data-loss risk before continuing.
- Select the cache RAID type and the M.2 SSDs that will provide the cache.
- Assign the amount of SSD capacity to use. Choose Max Capacity only when the entire SSD will remain dedicated to caching.
- Review the target volume, cache mode, RAID type, selected SSDs, and allocated capacity.
- Select Apply, then select Format when the data-erasure warning appears.
- Enter the current administrator password to begin building the cache.
Do not shut down the NAS or physically remove an M.2 SSD while the cache is being created.
Check Whether the Cache Is Helping
After the cache finishes building, return to:
Storage > Storage Pool & Volume > SSD Cache Management
Open the cache to view its usage and hit rate. Test it with the real workload that motivated the upgrade:
- Open the same group of small files several times.
- Browse a photo library after its thumbnails have been generated.
- Repeat a database or multi-user workflow.
- Compare responsiveness before and after the cache warms up.
A low hit rate means that most requested data is not being served from the SSD. Increasing the cache size will only help if the active working set is larger than the existing cache. If the files are rarely reused, a separate SSD pool is the more predictable solution.
If performance remains poor outside the cacheable workload, use our guide to diagnosing slow UGREEN NAS transfers. The limiting component may be the network connection, SMB settings, HDD array, client, or application rather than the cache.
How to Create a Separate SSD Storage Pool
A separate SSD pool is the better choice when the data itself needs SSD performance. Common examples include:
- Docker application data
- Virtual-machine disks
- Databases
- Frequently modified project files
- Active photo and video catalogs
- Scratch data that produces heavy random I/O
Keep the SSDs and HDDs in separate storage pools. That gives each type of storage a clear role and avoids building one RAID group from media with very different latency, throughput, and endurance characteristics.
Before creating the pool, decide how much protection the SSD data needs:
- One SSD in Basic mode: Full SSD capacity with no drive-failure tolerance.
- Two matched SSDs in RAID 1: Usable capacity equals the smaller SSD, with protection from one SSD failure.
- Two SSDs in RAID 0: Combined performance and capacity, but either SSD failing destroys the pool. Use it only for replaceable scratch data.
For a deeper comparison of capacity and failure tolerance, see our guide to UGREEN NAS RAID levels.
Create the SSD Pool
Important: Storage-pool creation formats the selected SSDs. Copy any existing data elsewhere before continuing.
- Open Storage.
- Go to Storage > Storage Pool & Volume.
- Select Create > Storage Pool.
- Select the unused M.2 SSDs.
- Choose the RAID type.
- Run the drive check before trusting new SSDs with application data.
- Set the volume capacity.
- Choose the file system:
- Select Btrfs when you need snapshot-based recovery for supported folders.
- Select EXT4 when the pool primarily handles large sequential files and snapshots are not required.
The file system cannot be changed directly after creation. Switching later requires reformatting the volume.
- Review the SSDs, RAID type, volume capacity, and file system.
- Select Create, acknowledge the formatting warning, and enter the administrator password.
Once the volume is ready, place latency-sensitive data on the SSD pool and retain high-capacity files on the HDD pool. For example, a video editor can keep current projects, project databases, and proxies on SSDs while moving completed footage and exports to HDD storage.
The SSD pool and HDD pool remain two storage destinations. Moving a file to the SSD pool consumes SSD capacity; unlike cache, the SSD pool holds the primary copy stored in that location.
How to Remove or Replace a Cache SSD Safely
Never pull an M.2 SSD while it is assigned as cache. Remove the cache through UGOS Pro first:
- Open Storage > Storage Pool & Volume.
- Open the HDD pool’s SSD Cache Management page.
- Select the cache.
- Select Remove.
- Wait until UGOS Pro confirms that the cache has been removed.
- Shut down the NAS.
- Disconnect power before removing or replacing the M.2 SSD.
Removing the cache correctly does not delete the original files from the HDD pool. Pulling the SSD first can corrupt the associated volume, especially when read-write cache still contains data waiting to be written to the HDDs.
Continue monitoring the SSDs through Storage > Hard Drive. Replace a cache SSD when its health status deteriorates, its error count rises, or it approaches the endurance limit specified by its manufacturer.
SSD cache and separate storage pools solve performance problems. Neither protects against deletion, ransomware, enclosure loss, or damage affecting the entire NAS. Maintain an independent backup of any data that cannot be replaced.
Frequently Asked Questions
Is SSD cache worth it on UGREEN NAS?
SSD cache is worth using when an HDD volume repeatedly serves small files, photo thumbnails, database data, or concurrent users. It provides limited benefit for one-time reads, media streaming, and continuous large-file transfers.
Does SSD cache increase NAS storage capacity?
No. SSD cache accelerates eligible data stored on an HDD volume but does not add usable storage capacity. Create a separate SSD storage pool if you want the SSDs to provide usable space.
Can one M.2 SSD create read-write cache?
No. One M.2 SSD can provide read-only cache. UGOS Pro requires two M.2 SSDs configured in RAID 1 for read-write cache.
Can SSDs and HDDs be used in the same RAID pool?
Keep SSDs and HDDs in separate roles. Use the M.2 SSDs as cache for an HDD volume or create a separate SSD storage pool. Combining both media types in one RAID group creates mismatched performance and endurance without delivering the predictable behavior of either layout.
