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Figure 14. VMware ESX Server 3.0 path information for iSCSI devices

The vmkmultipath command, when issued on an ESX 2.x server, provides details about the devices and

the number of paths attached to each device. At the service console of the VMware ESX server, type:

# vmkmultipath -q

Figure 15. VMware ESX Server 2.x path information through the native failover software

The most recently used MRU policy is the default policy for active/passive storage devices in ESX 2.x and

3.0. The policy for the path should be set to MRU for CLARiiON storage systems to avoid path thrashing.

When using the MRU policy, there is no concept of preferred path; in this case, the preferred path can be

disregarded. The MRU policy uses the most recent path to the disk until this path becomes unavailable. As

a result, ESX Server does not automatically revert to the original path until a manual restore is executed.

If you connect two ESX servers with path one from HBA1 to SPA, and path two from HBA0 to SPB, a

single LUN configured as a VMFS volume can be accessed by multiple ESX servers; in this example a

LUN can be accessed by both ESX servers.

If the HBA1-SPA path on ESX1 fails, it issues a trespass command to the array, and SPB takes ownership

of the LUN. If the path from HBA1-SPB on ESX2 then fails, the LUN will trespass back and forth between

the SPs, which could result in performance degradation.

When the CLARiiON LUN policy is set to MRU and an ESX server with two HBAs is configured so that

each HBA has a path to both storage processors, VMware ESX Server accesses all LUNs through one HBA

and does not use the second HBA. You can edit the path configuration settings so the other HBA is the

EMC CLARiiON Integration with

VMware ESX Server

Applied Technology 23

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