Windows file server virtual machine file transfer slowness

Products

• VMware vSphere ESXi

Issue/Introduction

• The file transfer client and server are both hosted on ESXi.
• The SMB2 protocol is in use.
• File transfers are slower than expected.
• Packet captures from the source VM and destination VM show no packet loss.
  A large chunk of packets is being transferred only after SMB protocol packets.

Environment

VMware vSphere ESXi 

Cause

This is not an ESXi network performance issue.
SMB protocol performance is not only limited to network speed, but also SMB flow control mechanism. 

Resolution

Refer to the following documentation for SMB performance tuning.

Performance tuning for SMB file servers
https://learn.microsoft.com/en-us/windows-server/administration/performance-tuning/role/file-server/smb-file-server

Slow SMB files transfer speed
https://learn.microsoft.com/en-us/troubleshoot/windows-server/networking/slow-smb-file-transfer