Microsoft Multipath I/O (MPIO) is an optional feature. By default, it is not installed in Windows Server. MPIO should be installed as a feature through Server Manager. This article describes the steps that you should follow to install and use the MPIO feature in Windows Server 2008 R2.

Symptoms. The code in Microsoft Windows that converts a hexadecimal device ID to an ASCII string may drop the most significant nibble in each byte if the byte is less than 0x10. (The most significant nibble is 0.) This causes different disks to be identified as the same disk by Multipath I/O (MPIO).

Fixes an issue in which an MPIO disk is removed unexpectedly when a PR_IN command fails. This issue occurs when the Failover Clustering feature is configured in a Windows Server 2008 R2 environment.

Learn about the terminology that Microsoft uses to describe software updates. Fixes an issue in which Windows Server 2012 R2 may lose its connection to the LUN with MPIO after you perform a storage controller failover.

This article describes a hotfix that provides a mechanism for Microsoft Device Specific Module (DSM) to notify Microsoft Multipath I/O (MPIO) that a particular path is back online. This hotfix adds a new notification type to the existing DsmNotification interface.

MPIO Paths. 4. Not Enforced. Virtual disks over MPIO per initiator on a stand-alone server. 64. Not Enforced. There is an initial delay after creating the disks before they appear to the Virtual Disk Service and the Disk Management snap-in because PnP first detects the devices and then MPIO detects the paths for each disk.

This issue occurs because the MPIO driver handles the IOCTL_MPIO_PASS_THROUGH_PATH_DIRECT control code that has an invalid MPIO path ID incorrectly. Resolution Hotfix information. A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article.

The iSCSI initiator may show the incorrect MPIO path state when you use storage arrays which support ALUA (asymmetric logical unit access). Symptoms. iSCSI initiator is not using MPIO_DSM_Path_V2 WMI Class to show the state, therefore, MPIO setting UI on iSCSI initiator cannot show and set the path state for ALUA.

Symptoms. Assume that you configure a Windows Server 2012 R2, Windows Server 2012 or Windows Server 2008 R2-based computer to use Microsoft Multipath I/O (MPIO) and Microsoft Device Specific Module (DSM). You connect a storage device to the computer by using redundant physical paths.

In this scenario, an MPIO path failover occurs incorrectly. The expected behavior is that the Mpio.sys driver can handle the transient device errors and does not trigger the MPIO path failover operation. Cause. The issue occurs because the mpio.sys driver incorrectly identifies an intermittent path failure as a device failure.