• Manages physical path claiming and unclaiming.
• Registers and de-registers logical devices.
• Associates physical paths with logical devices.
• Processes I/O requests to logical devices:
  • Selects an optimal physical path for the request (load balance)
  • Performs actions necessary to handle failures and request retries.
• Supports management tasks such as abort or reset of logical devices.

What’s new in  5.0 (regarding multipathing)?

Host Profiles have been extended to include support for storage multipathing.

vSphere Client operations

You can view the Storage Array Type and set the NMP pathing policy in Host and Clusters > Configuration tab > Storage (Hardware pane) > Click the Manage Paths link in the Device details section.

Path Policies explained:

• Most Recently Used (MRU) — Selects the first working path, discovered at system boot time. If this path becomes unavailable, the ESX/ESXi host switches to an alternative path and continues to use the new path while it is available. This is the default policy for Logical Unit Numbers (LUNs) presented from an Active/Passive array. ESX/ESXi does not return to the previous path when if, or when, it returns; it remains on the working path until it, for any reason, fails.Note: The preferred flag, while sometimes visible, is not applicable to the MRU pathing policy and can be disregarded.
• Fixed (Fixed) — Uses the designated preferred path flag, if it has been configured. Otherwise, it uses the first working path discovered at system boot time. If the ESX/ESXi host cannot use the preferred path or it becomes unavailable, ESX/ESXi selects an alternative available path. The host automatically returns to the previously-defined preferred path as soon as it becomes available again. This is the default policy for LUNs presented from an Active/Active storage array.
• Round Robin (RR) — Uses an automatic path selection rotating through all available paths, enabling the distribution of load across the configured paths.
  • For Active/Passive storage arrays, only the paths to the active controller will used in the Round Robin policy.
  • For Active/Active storage arrays, all paths will used in the Round Robin policy.

  Note: This policy is not currently supported for Logical Units that are part of a Microsoft Cluster Service (MSCS) virtual machine.

• Fixed path with Array Preference — The VMW_PSP_FIXED_AP policy was introduced in ESX/ESXi 4.1. It works for both Active/Active and Active/Passive storage arrays that support ALUA. This policy queries the storage array for the preferred path based on the arrays preference. If no preferred path is specified by the user, the storage array selects the preferred path based on specific criteria.

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CLI operations

~ # esxcli storage nmp [ENTER] will display the following namespaces, and allows for many useful native multipathing operations.  Useful for confirming GUI configurations.

Output from ~ # esxcli storage nmp device list command.

I know that’s not much but it’s all I got 🙂 .  Sayonara.

Gabe@networkdojo.net

Sources:
VMware KB 1011375
FC SAN Config Guide