When using MPIO on Windows Server in a multi-path SAN environment (iSCSI/Fibre Channel), the Round Robin load balancing policy did not behave correctly.
Even though the storage device exposed proper ALUA/TPG states, Windows was not following them – the Path State did not match the TPG State, and every second path switch attempt resulted in the I/O returning to the same path.
As a result, multipathing worked inconsistently and only one path was effectively used.
By default, Windows does not periodically verify path state unless the Path Verify Enabled option is enabled in the Device Specific Module (DSM).
If path verification is disabled, Windows does not refresh ALUA/TGP path priority data and therefore cannot make correct decisions for Round Robin routing.
Enable the “Path Verify Enabled” option in the DSM settings.
Go to
Server Manager → Tools → MPIO
Select the device / MPIO policy Round Robin
Click Details
In the DSM Details window, enable
Path Verify Enabled
Ensure the "Path Verify Period" is set (30 seconds is typical)
Once this setting is applied, Windows will actively verify the state of each path and update its Path State according to the TPG State provided by the storage array.
Path states now update correctly based on ALUA/TPG information
Round Robin properly alternates between optimized active paths
Failover and load balancing become fully functional and consistent
Windows no longer “ignores” optimized path
This setting is often overlooked and is disabled by default. However, without path verification, Round Robin may not operate correctly in ALUA-based storage environments.
Enabling Path Verify is therefore a key configuration step for stable and correct MPIO behavior on Windows Server.