ESXi 5.5 tip: Using LUNs and Windows VM’s – have them prepared for path failover

Path Failover and Virtual Machines

Path failover occurs when the active path to a LUN is changed from one path to another, usually because of a SAN component failure along the current path.

When a path fails, storage I/O might pause for 30 to 60 seconds until your host determines that the link is unavailable and completes failover. If you attempt to display the host, its storage devices, or its adapters, the operation might appear to stall. Virtual machines with their disks installed on the SAN can appear unresponsive. After failover is complete, I/O resumes normally and the virtual machines continue to run.

However, when failovers take a long time to complete, a Windows virtual machine might interrupt the I/O and eventually fail. To avoid the failure, set the disk timeout value for the Windows virtual machine to at least 60 seconds

Set Timeout on Windows Guest OS

Increase the standard disk timeout value on a Windows guest operating system to avoid disruptions during a path failover.

This procedure explains how to change the timeout value by using the Windows registry.


Back up the Windows registry.


1 Select Start > Run.
2 Type regedit.exe, and click OK.
3 In the left-panel hierarchy view, double-click HKEY_LOCAL_MACHINE > System > CurrentControlSet > Services > Disk.
4 Double-click TimeOutValue.
5 Set the value data to 0x3c (hexadecimal) or 60 (decimal) and click OK.

After you make this change, Windows waits at least 60 seconds for delayed disk operations to complete before it generates errors.

6 Reboot guest OS for the change to take effect.



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