Re: Inconsistent Windows virtual machine performance when disks are located on SAN datastores

Hi Duf,

Inconsistent Windows virtual machine performance when disks are located on SAN datastores
Details
Windows virtual machines may experience intermittent issues when stored on datastores presented from non-local storage. This issue may be encountered on virtual machines that use SAN, NFS or iSCSI storage.

These issues may include:
• Bluescreen errors
• Event ID: 9 messages in the Event Viewer
• This error reported in guest operating system:

The device, \Device\ScsiPort0, did not respond within the timeout period
• Virtual machine becomes unresponsive, halts, or is inaccessible from the console
Solution
Windows guest operating systems that are using virtual disks on non-local datastores might experience unexpected blue screens.
This issue occurs when the responses from the storage array take longer than the guest operating system expects to wait. The default disk timeout period in Windows is too short to handle the longer delays that can occur in a SAN, NFS, or iSCSI environment, and a blue screen error is the result of exceeding this timeout.
To resolve this issue, increase the disk timeout to 60 seconds in the Windows virtual machines by editing the Windows registry.



To increase the disk timeout value:
1. In the registry, go to HKEY_LOCAL_MACHINE/System/CurrentControlSet/Services/Disk.
2. Click Edit/Add value.
3. Set the value name to TimeOutValue.
4. Set the data type to REG_DWORD.
5. Set the data to 0x03c hex (or 60 decimal).
6. Reboot the virtual machine.
Note:
• Contact your Storage vendor to confirm whether a specific TimeOutValue setting has been identified for your particular environment.
• Increasing this disk timeout setting does not affect the performance of the guest operating system or virtual machine under normal operating conditions, but you must verify how the applications you are running in the guest operating system handle disk access delays.

Cheers,

warm regards,
Irra