How to Fix Slow UGREEN NAS Cloud Sync

Cloud sync cannot exceed your internet connection’s upload speed, even when your NAS has a 2.5GbE or 10GbE port. If a large file uploads quickly through your cloud provider’s website but runs substantially slower through Cloud Drives, focus on the Cloud Drives task, provider limits, and logs before changing NAS hardware.

If you have not created the task yet, start with our guide to set up an automated UGREEN NAS cloud backup.

Key Takeaways:

• Cloud sync speed is limited by internet upload speed, not the NAS’s 2.5GbE or 10GbE port.
• Compare local transfer, browser upload, and Cloud Drives upload using the same file to identify where the slowdown occurs.
• Small files, provider throttling, polling, and other NAS workloads can make Cloud Drives slower even when one large file uploads quickly.
• If browser uploads are fast but Cloud Drives is much slower, check the task settings, logs, provider limits, permissions, and other running workloads before changing hardware.
• Settings such as scheduling, file filters, and sync direction can reduce unnecessary work, but they cannot increase your ISP or cloud provider’s speed limit.

Is Cloud Sync Slow, or Is Something Else Syncing?

Before changing UGOS Pro settings, identify which operation is slow.

If wired local transfers are also slow, use our UGREEN NAS performance troubleshooting guide. Fixing the local bottleneck comes before troubleshooting Cloud Drives.

Measure the Upload Speed Available to Cloud Drives

1. Connect a computer to the same router as the NAS through Ethernet.
2. Pause large downloads, uploads, cloud tasks, and streaming on other devices.
3. Disconnect any VPN running on the computer.
4. Run the speed test two or three times.
5. Record the upload result, not only the download result.
6. Divide the upload Mbps by eight to estimate the best-case MB/s available to Cloud Drives.

If the router or NAS routes internet traffic through a VPN, bypass that route for the test or record it as part of the transfer path. A VPN can add latency, encryption overhead, congestion, or a slower route through its exit server.

Cloud upload speed is normally measured in megabits per second, or Mbps. File-transfer applications usually display megabytes per second, or MB/s.

Use this conversion:

Maximum upload throughput in MB/s = upload speed in Mbps ÷ 8

These are best-case figures. Protocol overhead, cloud API requests, encryption, file processing, provider throttling, and network interruptions reduce actual throughput.

If Cloud Drives runs close to the calculated ceiling, installing SSD cache, changing RAID, or buying a faster NAS will not materially improve the upload. The internet uplink is already the limiting layer.

Run Three Tests Before Changing UGOS Pro Settings

Use the same file for all three tests. Choose a unique file between 5GB and 10GB that has never been uploaded to the cloud account.

A newly recorded video or newly generated test file is better than a Linux image, installer, or file already stored in the destination. Reusing an existing file can trigger provider-specific conflict, version, or optimization behavior and make the comparison unreliable.

Keep the test conditions consistent:

• Use the same cloud account and destination folder.
• Keep the computer connected through Ethernet.
• Disable the computer’s VPN during the browser test.
• Pause unrelated uploads and cloud tasks.
• Do not change providers or test files between results.

Test 1: Copy the File Over the Local Network

Use wired SMB to copy the test file between the computer and NAS.

A healthy 1GbE connection commonly transfers one large file at approximately 100 to 110 MB/s. Faster Ethernet can exceed that figure when the computer, switch, NAS storage pool, and drives all support the higher speed.

If the local transfer is unexpectedly slow, the cloud is not the first problem to solve.

Test 2: Upload the File Through the Cloud Provider’s Website

From the same wired computer, upload the file directly through the Google Drive, OneDrive, or Dropbox website.

Record:

• Average upload speed
• Total upload time
• Whether the transfer stalls
• Whether the provider reports an error or usage limit

This test removes Cloud Drives from the path while retaining the same router, internet connection, cloud account, and provider destination.

Test 3: Upload the File Through Cloud Drives

In Cloud Drives:

1. Select the cloud connection.
2. Open Upload to Cloud Drive.
3. Click Select file.
4. Choose the same test file from the NAS.
5. Select the same cloud destination.
6. Start the upload and record its speed and completion time.

Compare the results:

What Happens If an Upload Is Interrupted?

After a router reboot, network outage, NAS restart, or provider error:

1. Open Cloud Drives.
2. Select the affected cloud connection.
3. Open Sync task > More > Details.
4. Check Log records for the interrupted file.
5. Run the task again if it did not continue.
6. Confirm that the destination file completed correctly.

Polling compares the file lists again. It does not guarantee that an individual file resumes from its previous byte position. An affected file may retry or restart, so check its actual progress before estimating how much transfer time remains.

Fix Slow UGREEN NAS Cloud Sync

Your Internet Upload Is the Limit

To prevent a large initial sync from disrupting the rest of the network:

• Pause other large uploads.
• Run the task outside working hours.
• Use router QoS or Smart Queue Management to preserve bandwidth for calls, browsing, and streaming.
• Avoid running several cloud tasks simultaneously.
• Break a multi-terabyte initial upload into separate folders.

Scheduling the task overnight reduces competition. It does not increase the maximum speed supplied by the ISP or cloud provider.

Small Files Are Slowing the Task

A 100GB video file and 100GB spread across 100,000 photos contain the same amount of data, but they do not require the same work.

Every individual file can require:

• Path and metadata comparison
• Cloud API requests
• Permission checks
• Conflict handling
• File creation at the destination
• Confirmation that the transfer completed

For a large initial sync:

1. Divide the source into logical top-level folders.
2. Sync one folder at a time.
3. Exclude temporary files, thumbnails, caches, and regenerable data.
4. Avoid multiple tasks scanning the same path.
5. Confirm each folder before starting the next one.

Creating one archive can make a one-time transfer faster because the cloud processes fewer objects. Do not use that approach for folders that require normal browsing, individual-file recovery, or continuing synchronization.

Cloud Drives Is Still Comparing File Lists

Cloud Drives may spend time scanning and comparing files before transferring new data. During this stage, the transfer rate can appear low even though the application is processing metadata.

For real-time synchronization, Polling Period periodically performs a broader comparison to identify changes that might have been missed during a network interruption.

Do not set an unnecessarily short polling interval. Frequent full comparisons increase repeated scanning and can prevent the NAS drives from entering hibernation.

If the folder changes only at predictable times, scheduled synchronization may be a better fit than continuous real-time monitoring.

The Cloud Provider Is Throttling Requests

Open the Cloud Drives task details and logs before treating provider throttling as a NAS hardware problem.

Use:

• Cloud Drives > [cloud connection] > Sync task > More > Details
• Cloud Drives > [cloud connection] > Log records

Look for repeated retries, authorization failures, unavailable paths, insufficient capacity, and rate-limit responses.

Google documents a 750GB upload-and-copy limit within 24 hours for Workspace users. Users who reach the limit cannot upload or copy additional files until it refreshes. See the official Google Drive API limits.

Google does not clearly document that same limit for every personal Google account on that page. Personal accounts can encounter other service or account restrictions, so check the Cloud Drives log for a quota or rate-limit response rather than assuming that the Workspace threshold applies.

Microsoft documents 429 and 509 responses in its Microsoft Graph error guidance. Dropbox can return a Retry-After period with a 429 response, as explained in the Dropbox API error guide.

More Ethernet bandwidth or SSD cache does not remove a provider-side limit. Wait for the retry period, reduce overlapping work, confirm account capacity, and check the provider’s service status.

Another NAS Workload Is Competing for Resources

Cloud synchronization uses network bandwidth, storage I/O, CPU time, and memory. Check whether the NAS is also performing:

• RAID synchronization or rebuilding
• Data Organizing
• Photo indexing or AI analysis
• Media-library scanning
• Another backup or synchronization task
• A large download
• Antivirus scanning
• A container or virtual machine with sustained disk activity

Do not interrupt RAID rebuilding, RAID synchronization, or Data Organizing merely to improve a cloud benchmark. Allow the storage operation to finish, then repeat the same upload test.

Pause optional tasks one at a time. If Cloud Drives becomes faster after one task stops, you have identified resource contention rather than an internet problem.

Before retesting, update UGOS Pro and Cloud Drives. Pause the cloud task first, then use:

Control Panel > Update & Restore > System Update

Update Cloud Drives through the App Center. System updates stop application services, so do not begin an update in the middle of an important transfer.

The Task Is Misconfigured

A task that repeatedly retries failed files can look slow even when successful transfers run normally.

Check:

• Available capacity on both the NAS and cloud account
• Cloud and NAS paths
• Read and write permissions
• File filters
• Conflict-handling rules
• Sync direction
• Expired account authorization
• Duplicate tasks using the same source and destination
• Unsupported file names or path structures
• Failed-file records in the task log

If the task stops, skips files, or repeatedly fails at the same point, use our guide to fix a failed NAS backup task.

Which Cloud Drives Settings Affect Performance?

Do not look for an upload-thread control or enable SSD cache solely for Cloud Drives. Neither is a verified general-purpose fix for slow UGREEN NAS cloud synchronization.

What to Collect If Cloud Drives Remains Slow

If the browser upload is fast but Cloud Drives remains substantially slower with the same unique file, collect the following information:

• Cloud provider
• Sync direction
• NAS source path
• Cloud destination path
• Measured internet upload speed
• Browser-upload speed
• Cloud Drives upload speed
• Test-file size
• Approximate file count in the affected folder
• UGOS Pro version
• Cloud Drives version
• Whether a VPN was active on the NAS or router
• Other tasks running during the test
• Exported Cloud Drives logs
• Exact error code and timestamp
• Whether an interrupted file resumed or restarted

For questions about TLS, cloud authorization, or encrypting files before upload, follow our guide to secure NAS-to-cloud transfers.