System information

Figure 6-1. Manual Load Balancing with Fibre Channel

storage array

ESX/ESXi

SP1 SP2

3 421

FC switch

HBA2HBA1 HBA4HBA3

For load balancing, set the preferred paths as follows. Load balancing can be performed with as few as two

HBAs, although this example uses four.

For LUN 1: HBA1-SP1-LUN1

For LUN 2: HBA2-SP1-LUN2

For LUN 3: HBA3-SP2-LUN3

For LUN 4: HBA4-SP2-LUN4

With active/passive arrays, you can perform load balancing if the array supports two active paths and the HBA

ports can access both SPs in an array.

NOTE Active/passive arrays use the MRU path policy which does not have a preferred path. If a path failure

occurs, there is no failback. As a result, static load balancing can become out of balance over time.

Path Failover

Path failover refers to situations when the active path to a LUN is changed from one path to another, usually

because of some SAN component failure along the current path. A server usually has one or two HBAs and

each HBA is connected to one or two storage processors on a given SAN array. You can determine the active

path, the path currently used by the server, by looking at the LUN’s properties.

When an FC cable is pulled, I/O might pause for 30-60 seconds until the FC driver determines that the link is

unavailable and failover has occurred. As a result, the virtual machines, with their virtual disks installed on

SAN storage, can appear unresponsive. If you attempt to display the host, its storage devices, or its adapter,

the operation might appear to stall. After failover is complete, I/O resumes normally.

In case of disastrous events that include multiple breakages, all connections to SAN storage devices might be

lost. If none of the connections to the storage device is working, some virtual machines might encounter I/O

errors on their virtual SCSI disks.

Set Operating System Timeout

You might want to increase the standard disk timeout value so that a Windows guest operating system is not

extensively disrupted during failover.

For Windows 2000 and Windows Server 2003 guest operating systems, you can set operating system timeout

using the registry.

Prerequisites

Before you begin, back up your Windows registry.

Fibre Channel SAN Configuration Guide

64 VMware, Inc.