How to Fix UGREEN NAS Backup Failures

When a UGREEN NAS backup fails, record the exact error and open the task log before changing settings. Most failures occur at one of three points: the source cannot be read, the transfer connection is interrupted, or the destination cannot accept more data.

Deleting the task, clearing its configuration, or removing the existing destination should be a last resort. Those actions can erase useful diagnostic evidence or remove the most recent usable backup.

LD;DR

• Start with the backup log, not by deleting the task. Record the full error, last successful run, source, destination, and failure point before changing settings.
• Most failures come from the source, transfer path, or destination. Check file access and permissions, client or network connectivity, and whether the target is mounted, writable, and has enough space.
• A repeatable failure point is useful evidence. If the backup stops at the same percentage, use the log and a small test task to isolate the affected file, folder, connection, or capacity issue.
• “Service Error” should be repaired in stages. Restart Sync & Backup, restart the desktop client, check the Windows syncSpace process, and reset local configuration only if simpler fixes fail.

Preserve the Existing Backup and Error Evidence

Start by pausing repeated attempts if the same task continues to fail. Then record:

• The task name and backup type
• The complete error message and error code
• The date and time of the failure
• The last successful run
• The selected source and destination
• The percentage or file where the task stopped
• The available capacity at the destination

Take screenshots of the task settings and error message. Keep the existing backup destination intact while you investigate.

Identify Which Backup Task Failed

Different UGREEN backup methods depend on different devices, applications, and connections.

If the task has never worked, verify that its initial configuration is complete. Our guides cover backing up a computer to UGREEN NAS, backing up UGREEN NAS to an external drive, and automating NAS-to-cloud backups.

Once you know which workflow failed, the task log should determine which layer to examine next.

Read the Backup Log Before Changing Settings

In UGOS Pro, open:

Sync & Backup > Back up & Restore > locate the failed task > More > View backup log

Find the last successful action and the first failed action. The useful evidence is usually the file path, connection message, permission error, capacity warning, or service status surrounding the failure.

Use the log to separate the problem into three layers:

If the interface displays Error Code 1, record the full accompanying message. The number alone does not provide enough information to select a repair. The task log and the point at which the task failed are more useful than guessing what the code represents.

Fix the Failure Based on Where the Task Stops

The Backup Task Cannot Be Created

A task that fails during creation usually cannot validate its source, destination, or connection.

Check that:

1. The source folder exists and the account creating the task can open it.
2. The destination folder exists and allows that account to write data.
3. An external drive appears in Files and is writable.
4. A remote rsync or WebDAV destination is online.
5. The entered address, port, username, password, and destination path are correct.
6. The destination has enough capacity for the selected data.

UGREEN NAS uses port 873 as the default rsync port. The default WebDAV ports are 5005 for HTTP and 5006 for HTTPS. Use the configured value if the destination administrator changed these defaults.

Run the connection test before saving a remote task. If authentication succeeds but task creation still fails, verify that the remote account has permission to create and modify files inside the selected destination folder.

A Scheduled Computer Backup Does Not Start

The Backup this computer workflow requires the UGREEN NAS desktop client to remain running. Exiting the client stops the backup process.

Before waiting for the next schedule:

1. Wake the computer and connect it to the network.
2. Open the UGREEN NAS desktop client.
3. Confirm that the NAS is connected.
4. Open Sync & Backup and verify that the task is enabled.
5. Run the task manually.

A laptop that is asleep, shut down, or disconnected cannot send its files to the NAS. If the manual run works but scheduled runs do not, examine the computer’s sleep schedule and whether the UGREEN NAS client is still running at the scheduled time.

The Backup Stops at the Same Percentage

A repeatable stop point narrows the investigation.

Open the task log and identify:

• The last file transferred successfully
• The first file or folder that produced an error
• Whether the message concerns reading, permissions, connection, or capacity
• Whether the failure occurs at the same time or after the same amount of transferred data

Next, create a temporary task containing a small folder with several unique test files. Send it to a new destination folder.

If the small task succeeds, the backup service and destination are broadly functional. Return to the original log and test the affected source folder separately. For a very large library, backing up folders in stages also makes the failing source easier to isolate.

The Backup Completes but Some Files Are Missing

A completed task status does not prove that every expected file reached the destination.

Compare the selected source with the destination and review the log for unavailable or skipped items. If the message says that some files were unavailable during the last backup:

1. Confirm that each affected source path still exists.
2. Open the file using the same computer or NAS account involved in the task.
3. Verify that the account can read its parent folder.
4. Copy one affected file to the destination manually.
5. Run a temporary backup containing only the affected folder.

Also confirm that the missing files were inside the task’s selected source. Adding a new folder elsewhere on the computer does not add it to an existing task.

For important data, open several files from the backup destination rather than checking filenames alone. A file that appears in the folder but cannot be opened is not a usable backup.

The Destination Reports Insufficient Capacity

Check the destination’s available capacity and compare it with the amount of data still waiting to be backed up.

The Backup this computer workflow uses incremental backup and retains files at the destination after they are deleted from the source. This protects against accidental deletion, but it also means the backup can grow larger than the computer’s current library.

When the destination is full:

• Preserve the most recent usable backup.
• Remove unrelated data before touching backup content.
• Move the task to a larger destination when necessary.
• Review whether old backup data still needs to be retained.
• Avoid deleting the only restorable copy simply to make the next task pass.

For Btrfs storage spaces, UGOS Pro 1.16.0.0042 and later includes Reclaim Storage Space for cases where the system reports free capacity but write operations still fail. This addresses reclaimable Btrfs space; it does not create capacity when the stored data genuinely fills the destination.

A Remote rsync or WebDAV Backup Cannot Connect

Check the destination before changing the source task.

Confirm that:

1. The remote NAS or server is powered on.
2. Its rsync or WebDAV service is enabled.
3. The hostname or IP address is correct.
4. The port matches the destination configuration.
5. The account credentials are valid.
6. The account can write to the selected destination.
7. Any firewall between the two systems permits the connection.

Test the destination from the same network path used by the NAS. A service that works from a computer on the destination’s local network may still be unreachable from the source NAS.

If the task connects and transfers data but performs slowly, follow the separate NAS cloud-sync troubleshooting process. A slow working task and a failed connection require different diagnostics.

Fix a Sync & Backup “Service Error”

A Service Error can occur when the NAS application, desktop client, or local syncSpace process is not running correctly.

Work through these repairs in order.

1. Restart Sync & Backup

Open the UGREEN NAS desktop client and go to App Center. Select Sync & Backup, choose Disable, and then select Enable to restart the sync service.

2. Restart the Desktop Client

Fully exit the UGREEN NAS desktop client and open it again.

On Windows, right-click the UGREEN NAS icon in the system tray and select Exit. Closing only the visible window may leave the background process running.

3. Check the Windows syncSpace Process

On Windows, press Ctrl + Shift + Esc to open Task Manager and search for syncSpace.

If the process is not running:

1. Check the Recycle Bin and antivirus quarantine to see whether the program was removed or blocked.
2. Open this directory:

C:\Program Files\UGREEN NAS\resources\public\win32\syncspace

3. Confirm that syncspace_pro.exe is present.

If the executable is missing, repair or reinstall the UGREEN NAS desktop client before recreating backup tasks.

4. Reset the Local Sync & Backup Configuration

Use this step only when syncSpace is running but Service Error continues after restarting the application and desktop client.

First, save screenshots of the existing task settings and fully exit the UGREEN NAS desktop client.

Windows

Open File Explorer, enter the following path, and press Enter:

%appdata%\UGREEN_Nas_Pro\apps\syncSpace

macOS

Hold Option, open the Finder Go menu, and select Library. Navigate to:

Application Support/com.ugreen.desktop/UGREEN_Nas_Pro/apps/syncSpace

Inside the syncSpace directory, locate the folder named after the affected NAS serial number. Open that device folder and delete the .config folder inside it.

Reopen the UGREEN NAS desktop client and check whether Service Error has cleared. Resetting the configuration can require local task information to be configured again, so it should not be the first response to an ordinary file, permission, connection, or capacity error.

Verify the Repair With a Backup and Restore

A task reporting success is only the first half of the test. A working backup must also restore usable data.

Use this controlled validation process:

1. Create a folder containing several unique test files.
2. Include at least one document, photo, and larger file.
3. Run a manual backup to a new destination folder.
4. Confirm that the task log reports success.
5. Restore one file to a different location.
6. Open the restored file and verify its contents.
7. Delete a test file from the source and check whether the destination behaves as expected for the selected backup mode.

Only resume the full schedule after both the backup and restore tests succeed.

Continue checking the task history after the next several scheduled runs. A single successful test does not resolve a recurring sleep, connection, or capacity problem unless the normal schedule also works.

When Should You Stop Retrying the Backup?

Stop making repeated attempts when:

• The destination storage system shows Critical.
• Multiple drives disappear from the storage pool.
• A drive reports serious SMART or health warnings.
• The NAS becomes unstable during file access.
• The only remaining copy of the data is on the affected source or destination.
• Files disappear or become corrupted after each attempt.
• The last backup cannot be restored.
• The repair would require deleting the existing backup before another copy exists.

At that point, preserve the hardware state and avoid unnecessary writes. Follow the appropriate UGREEN NAS data-recovery process before rebuilding the task or storage pool.

Frequently Asked Questions About UGREEN NAS Backup

What does Error Code 1 mean on a UGREEN NAS backup task?

Error Code 1 alone does not identify one specific repair. Record the complete error message, open the task-specific backup log, and determine whether the failure occurred while validating the source, starting the service, connecting to the destination, or writing data.

Why does my UGREEN NAS backup fail at the same percentage?

A repeated stopping point usually indicates that the task reaches the same source item or destination condition on each attempt. Check the last successful and first failed entries in the backup log instead of assuming the percentage proves that one file is corrupt.

Why did the backup complete with files missing?

The task may have completed with exceptions, or the missing files may fall outside the selected source. Compare the source and destination, review the log for unavailable files, and restore several files to confirm that the backup is complete and readable.

Should I delete and recreate a failed backup task?

Not initially. Preserve the task settings, backup destination, and logs while checking the source, connection, permissions, service status, and capacity. Recreate the task only after simpler repairs fail and another usable copy of the data exists.