> Protect Against Connection Failures To SAN Devices
> When a cable is pulled, I/O freezes for approximately 30-60 seconds, until the SAN driver determines that the link is down, and failover occurs. During that time, the virtual machines (with their virtual disks installed on a SAN) may appear unresponsive, and any operations on the
> /vmfs directory may appear to hang. After the failover occurs, I/O should resume normally.
> Even though ESX Server's failover feature ensures high availability and prevents connection loss to SAN devices, all connections to SAN devices may be lost due to disastrous events, that include multiple breakages. If all connections to the storage device are not working, then the virtual machines will begin to encounter I/O errors on their virtual SCSI disks. Also, operations in the /vmfs directory may eventually fail after reporting an I/O error.
> To set up disk timeout:

> • | For QLogic cards, consider adjusting the PortDownRetryCount value in the QLogic BIOS. This value determines how quickly a failover occurs when a link goes down. If the PortDownRetryCount value is, then a failover typically takes a little longer than multiplied by 2 seconds. A typical recommended value for is 15, so in this case, failover takes a little longer than 30 seconds. For more information on changing the PortDownRetryCount value, refer to your QLogic documentation.

> • | For the Windows 2000 and Windows Server 2003 guest operating systems, consider increasing the standard disk TimeOutValue so that Windows will not be extensively disrupted during failover. For a VMware environment, the Disk TimeOutValue must be set to 60 seconds. o

> 1. | Select Start > Run, type regedit.exe, and click OK.

> 2. | In the left panel hierarchy view, double-click HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Disk.

> 3. | Do one of the following:

> • | Select TimeOutValue if it exists and set the Data value to x03c (hexadecimal) or 60 (decimal). By making this change, Windows waits at least 60 seconds, for delayed disk operations to complete, before generating errors.

> • | If TimeOutValue does not exist, select New from the Edit Menu and then DWORD value. In the Name field, type TimeOutValue and then set the Data value to x03c (hexadecimal) or 60 (decimal).

> 4. | Click OK and exit the Registry Editor program.

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