Several reasons might prevent files from syncing correctly between Synology Drive and Drive clients. This article explains these possible causes and provides corresponding solutions.

View logs for unsynced events

Synology Drive Client supports logging for unsynchronized events¹. To view the files that were not synced and the reasons for their failure, go to Synology Drive Client > Logs.

For more information on the cause of files or folders not syncing, please refer to the rest of this article section.

You have set up a sync rule for the sync task

You have set up a sync rule to exclude specific files from syncing.

For Synology Drive Client:

Go to Synology Drive Client > Sync Tasks > select a task > Sync Rules.

• File Filter: Check if you have set a maximum file size limit or excluded specific file extensions from synchronization.
  
• Folder: Folders not selected here will not be synchronized.
  

For Synology Drive ShareSync:

Go to Synology Drive ShareSync > select a server > Synced folders > select an enabled task > Edit.

• File filter: Check if you have set a maximum file size limit or excluded specific file extensions from synchronization. Only selected items will be synced.
  
• Folder: Check the Folder-Based Selective Sync setting. Folders not selected here will not synchronize.
  

For Synology Drive Server:

Go to Synology Drive Admin Console > Settings > User Sync Profiles > select a profile > Edit. If your account is listed under Applied User, the File Filter rules of this profile will apply to your account.

Your file types, file names, or device types are not supported

Check if your file name, file type, or attributes meet the circumstances described in the Sync Task Rules and Backup Task Rules section. By default, Synology Drive will not sync these files and folders.

Below are some common reasons for unsupported synchronization, along with methods to check or resolve these problems:

File names containing unsupported special characters

The folder or file name containing following characters will not be synchronized:

• Unsupported characters in Windows environments include:
  • File name starting with a tilde (~)
  • Path containing the following characters: * : ? \ / " < > |
• Unsupported characters in macOS and Linux environments include:
  • File name starting with a tilde (~)
  • Path containing the following characters: \ /

Avoid using unsupported special characters in file names. Since Synology Drive can be accessed by multiple operating systems, and file naming conventions may vary, this can cause issues. Files or folders with unsupported special characters in their names will not synchronize.

File name path exceeds the limitation

File names and paths that exceed the limitations will not be synchronized:

• Windows: The name or path of the folder/file is longer than 247 characters
• macOS:
  • The path of the folder/file is longer than 768 characters
  • The file name is longer than 255 characters
• Linux:
  • The path of the folder/file is longer than 2,048 characters
  • The file name is longer than 255 characters

Ensure that the file name path doesn't exceed the limit for each operating system. You can use tools to check the total character length of the file path. For example, in a Windows environment, you can use Notepad++. Simply paste the complete file path and name (including the extension) into Notepad++, and it will display the total character length.

The file contains unsupported file attributes

In a Windows environment, files or folders containing any of the following attributes will not be synchronized:

• OFFLINE
• REPARSE_POINT
• SYSTEM
• TEMPORARY

Remove unsupported attributes from the file. To view the file's attributes, right-click on the unsynced file, select Properties and go to the Details tab. In the example below, the file contains the SYSTEM (SA) attribute, which is not supported for syncing. Refer to this Microsoft article² and use the "attrib" tool to remove unsupported attributes.

The file you wish to sync is restricted

• Make sure the file is not opened in other applications. Files opened in other applications may be locked and unable to synced.
• Make sure you have permission to access the files you want to sync. If you are not an administrator, ask an administrator to check the file's permission settings for you.
• Make sure the permissions for the files or folders are not set to Read only.

Antivirus software or firewalls are enabled on your computer

• Add Synology Drive Client and the sync folder to the antivirus program's allow list.
• If antivirus software detects downloaded files as potentially harmful, they may not synchronize. Refer to this article for resolutions.

The number of files you wish to sync exceeds the recommended amount

Depending on the CPU model, each Synology NAS has a different maximum number of files it can sync simultaneously. Refer to the product specification page for your Synology NAS model to find the recommended limit³. Follow the steps below to resolve this issue:

1. Go to File Station, right-click on the folder that is not syncing, and select Properties to view how many files it contains.
   
2. Review your files and synchronization rules. If you exceed the recommended file limit mentioned on the product specifications page, consider disabling some folders in the Synology Drive Admin Console. This will reduce the number of files being synchronized and lessen the server workload.
3. If the synced folders have many sub-folders, consider reorganizing your folder structure. Sync only essential folders to reduce server workload. For example, move unnecessary folders and files to a shared folder that isn't set as a team folder in the Synology Drive Admin Console. For more information on team folder management, refer to this help article.

The files displayed in Synology Drive and File Station are inconsistent

When Synology Drive Server does not correctly index files, inconsistencies may occur between files displayed in Synology Drive and File Station. This can prevent files from syncing. When this happens, please check whether files not displayed on Synology Drive are supported for syncing. Then, refer to this article for resolution.

Contact Technical Support

If none of the above methods resolve the issue, please contact Synology Technical Support. This requires signing in to your Synology Account. To help diagnose the issue, make sure to include your system log files, the Synology Drive Client log, and the paths and filenames of about 1-5 files that can't be synced.

To obtain Synology NAS system log files:

1. Sign in to DSM with an administrator account.
2. Go to Main Menu > Support Center > Support Services.
   • For DSM 5.x and 6.x: Under Log Generation, select System and Synology Drive Server, then click Apply and Generate logs.
   • For DSM 7.0 and above: Under Log Generation, select Synology Drive Server, then click Apply and Generate logs.

To obtain Synology Drive Client logs:

1. Add another file to the sync folder that cannot be synced to reproduce the same error. This ensures that the sync error is recorded by the Synology Drive Client.
2. Follow these steps to obtain Synology Drive Client logs.
   • On Synology Drive Client:
     1. Go to Windows system tray or Mac menu bar and left-click once on the Synology Drive Client icon. Click the ellipsis at the bottom-right corner, and go to Troubleshoot > Export diagnostic log.
     2. Click Export. By default, the logs will be saved to your download folder.
   • On your computer:
     • For Windows 7 and above:^4 5 Copy and compress the files in the path below before sending them to Synology.
       
       C:\Users\[user_name]\AppData\Local\SynologyDrive\log
     • For Mac: Open Terminal on your Mac. Enter "terminal" in Spotlight (magnifying glass icon) on the upper-right corner, and enter the command below to compress the file. The compressed Synology Drive Client log will be saved to the desktop.
       • For Synology Drive Client 3.1 and earlier:
         
         cd ~/.SynologyDrive/log && tar -czf ~/Desktop/synologydrive.tgz *
       • For Synology Drive Client 3.2 and above:
         
         cd ~/Library/Application\ Support/SynologyDrive/log && tar -czf ~/Desktop/synologydrive.tgz *