1. Diagnosing the Problem

  1. Check Network Speed

    • Use iperf3 to measure network throughput between the two Macs.

      # On Mac B (SMB Server)
iperf3 -s

# On Mac A (Client)
iperf3 -c <Mac B's IP>

    • If the speed is close to 1Gbps, the network is performing as expected.

    • If it’s significantly lower (e.g., below 500 Mbps), there may be a bottleneck in the network hardware or cabling.

  2. Check Latency with ping

    • Use ping to measure round-trip time between Mac A and Mac B.

      ping -c 10 <Mac B's IP>

    • A response time below 1ms is expected.

    • If latency is higher, check for network congestion or interference.

  3. Test File Transfer Speed

    • Copy a large file using rsync to measure SMB performance.

      rsync --progress /Volumes/SharedDrive/testfile.bin ~/Desktop/

    • A well-performing SMB connection on a 1Gb network should achieve speeds close to 110 MB/s.

2. Diagnosing SMB-Specific Issues

SMB Version

Check which SMB version is being used.

smbutil statshares -a

  • If the SMB version is 2.1, it may not be negotiating SMB 3 properly.

Forcing SMB 3

  • Modify /etc/nsmb.conf to enforce SMB 3.

    [default]
protocol_vers_map=6

  • Restart SMB services:

    sudo launchctl stop com.apple.smbd
sudo launchctl start com.apple.smbd

3. Optimizing macOS for SMB

Finder Metadata Indexing

  • Finder generates thumbnails and previews, which can slow down SMB access.

  • Disable animations and metadata caching:

    defaults write com.apple.finder DisableAllAnimations -bool true
killall Finder
Opportunistic Locking

  • Disabling OpLocks can improve performance. Add to /etc/nsmb.conf:

    [default]
oplocks=no

  • Restart SMB services:

    sudo launchctl stop com.apple.smbd
sudo launchctl start com.apple.smbd
Spotlight Indexing

  • Prevent Spotlight from indexing SMB shares:

    sudo mdutil -i off /Volumes/SharedDrive

  • Permanently exclude the SMB share from indexing:

    echo "/Volumes/SharedDrive" >> ~/.metadata_never_index
Disabling SMB Signing

SMB signing adds security but reduces performance. It is enabled by default on macOS, which can impact file transfer speeds [1].

  1. Check if SMB signing is enabled:

    sysctl -a | grep net.smb.fs.kern.signed

    • If it returns 1, signing is enabled.

  2. Disable SMB signing:

    [default]
signing_required=no

  3. Restart SMB services:

    sudo launchctl stop com.apple.smbd
sudo launchctl start com.apple.smbd

4. Testing Performance After Optimization

  • Re-run iperf3 to verify network speeds.

  • Use cp or rsync to test file transfer speeds.

  • If performance is still slow, consider using NFS instead of SMB for macOS-to-macOS file sharing [2].

5. Expected Improvements

  • Enabling SMB 3: 10-20% improvement in speed.

  • Disabling SMB signing: Up to 2x faster transfers.

  • Disabling Finder previews: Faster browsing of network shares.

  • Preventing Spotlight indexing: No lag when accessing files.

  • Using rsync instead of Finder: More consistent transfer speeds.

After applying these optimizations, SMB performance should be significantly improved, reducing latency and maximizing transfer speeds across the 1Gb network.