A disk may not come online if only non-optimized paths are available on Windows Server 2008 and Server 2008 R2

Applies to: Windows Server 2008 StandardWindows Server 2008 EnterpriseWindows Server 2008 Datacenter


Consider the following scenario:

In an MPIO/ALUA configuration on Windows Server 2008 and Server 2008 R2 where only non-optimized paths are available, a disk may not come online.


This occurs because the default MPIO policy for ALUA capable controllers when using the Microsoft DSM is Round Robin with Subset (RRwS), and this policy does not allow a disk to come online without an optimized path being available.


If you have a configuration where you need to function with only non-optimized paths available, use one of the following MPIO policies:

·         Least Queue Depth

·         Failover Only

·         Weighted Paths

·         Least Blocks

More Information

To change the default policy on Windows Server 2008 R2, use mpclaim.exe as documented in the following TechNet articles:



For Windows Server 2008 you need to use a script such as the one referenced in the following post, because the version of mpclaim.exe for Windows Server 2008 does not support the commands necessary.