What can I do when the file transfer via Windows (SMB/CIFS) is slow?

To ensure the data transfer speed between your Synology NAS and Windows Explorer via SMB/CIFS, please refer to this article to check if you have applied appropriate network settings, and make sure both your Synology NAS and client devices are running smoothly. You can also follow this article to hide the preview pane and thumbnail previews of your Windows Explorer and see if the transfer speed is improved.

If the problem persists after you check all the items listed above, please try the following solutions:

On your Synology NAS

Network Settings:

    • In DSM > Control Panel > Network > Network Interface, check the MTU value of the interface currently in use, and make sure the settings are identical with the client computer. Untick Set MTU value manually to return to the default MTU value if the problem persists.
    • Enable DHCP:
      1. In DSM > Control Panel > Network > Network Interface, select the interface currently in use, and click Edit.
      2. Tick Get network configuration automatically (DHCP).
      3. Enable DHCP on your client computer.
      4. Connect your NAS and client computer directly with a cable without a router or switch in between.

Note:

  • To check the IP address of your NAS, please launch Synology Assistant on the client device for search. The IP address should be 169.254.X.X. To download Synology Assistant, please visit our Download Center, determine your product type, and go to the Desktop Utilities tab.
  • In DSM > Control Panel > Network > Traffic Control, disable the active rules that may affect SMB transfer speeds.

File Sharing:

  • If your Synology NAS has joined a domain where Directory Server for Windows Domain is enabled, go to Control Panel > Domain/LDAP > Domain > Domain Options, set Enable server signing as Disable, and disable server signing on the client device as well.

    Note:

    • This action may compromise security.
  • Please check if the source/destination folders are encrypted. The encryption of folders may significantly increase the CPU workload and decrease the data transfer rate.
  • It can be time-consuming if each piece of data needs to be verified through checksum. For a better transfer rate, you can and leave Enable data checksum for advanced integrity unticked when creating a new shared folder in DSM > Control Panel > Shared Folder.
  • In DSM > Control Panel > File Services > SMB/AFP/NFS, click Advanced Settings. Select SMB2 with large MTU as the Maximum SMB protocolSMB2 as the Minimum SMB protocol, and tick both Enable opportunistic Locking and Enable SMB2 lease.
  • Collecting debug logs may affect system performance. In DSM > Control Panel > File Services > SMB/AFP/NFS, you can click Advanced Settings, and untick Collect debug logs.
  • Temporarily disable indexing services:
    • File indexing: Launch Universal Search, click Preferences (the cogwheel icon), and disable file indexing on all shared folders.
    • Media indexing: In DSM > Control Panel > Indexing Service, click Indexed Folder, and disable the indexing folders.

System Status:

  • Launch Resource Monitor to check the system performance. You may need to end CPU-demanding, memory-demanding, and I/O-demanding packages for a better read/write performance.
  • If you are familiar with Linux, check the direct read/write speed of your drive with dd command:
    echo 3 > /proc/sys/vm/drop_caches; time dd if=/dev/sda1 of=/dev/null bs=1M count=1K

    You can then determine if you need to replace any defective drives.

  • Launch Storage Manager and go to the Volume page to check the remaining storage space. If the volume space is about to be used up, you may need to free up some space for better read/write performances.
  • Launch Storage Manager and go to the Storage Pool page. If the volumes are ExpandingRepairing, or performing any other actions, please wait until the process is complete, and then continue to transfer files.
  • Launch Storage Manager and go to the HDD/SSD page. Select a drive, and go to Health Info > S.M.A.R.T. to run a test. Replace unhealthy drives if needed.
  • Disable all scheduled backup tasks and any scheduled tasks for Recycle Bin (especially on Btrfs volumes).
  • Due to limited CPU capabilities, RAID 0 and RAID 1 volumes will have lower read/write performance on certain models of J series or Value series.

On the Client Device

    • When transferring files, make sure the client computer is not busy and is not running any .exe files.
    • Try different file protocols (e.g. AFP, CIFS, FTP, HTTP) to check if the problem is exclusive to Windows file services. If not, please refer to this article to check the system status of your NAS and client device.
    • Enable DHCP:
      1. Enable DHCP on your client computer.
      2. Connect your NAS and client computer directly with a cable without a router or switch in between.
      3. In DSM > Control Panel > Network > Network Interface, select the interface currently in use, and click Edit.
      4. Tick Get network configuration automatically (DHCP).

Note:

  • To check the IP address of your NAS, please launch Synology Assistant on the client device for search. The IP address should be 169.254.X.X.
    To download Synology Assistant, please visit our Download Center, determine your product type, and go to the Desktop Utilities tab.
  • Make sure the MTU settings are identical with your Synology product.
  • Disable all firewall or antivirus software.

Contact Us

If none of the solutions above mitigate the low-speed file transfer issue, please send us a copy of your system log through a support ticket. The log files will provide us with more technical information on your system, and help us clarify the problem.

Note:

  • To learn more about how we collect, use, and protect your data sent via a support ticket, please check out the “Technical Support” section in our Privacy Statement.

To generate logs and send a support ticket:

  1. Sign in to DSM as an administrator.
  2. Launch Support Center, and go to Support Services.
  3. Under Log Generation, select needed items, and click Generate Logs.
  4. Go to the Contact Support page, follow the steps to submit a support ticket, and remember to attach the generated .dat file.

Article from: https://www.synology.com/en-vn/knowledgebase/DSM/tutorial/File_Sharing/What_can_I_do_when_the_file_transfer_via_Windows_SMB_CIFS_is_slow