When you start your ESX host or rescan your storage adapter, the host discovers all physical paths to storage devices available to the host. Based on a set of claim rules defined in the /etc/vmware/esx.conf file, the host determines which multipathing plug-in (MPP) should claim the paths to a particular device and become responsible for managing the multipathing support for the device.

By default, the host performs a periodic path evaluation every 5 minutes causing any unclaimed paths to be claimed by the appropriate MPP.

The claim rules are numbered. For each physical path, the host runs through the claim rules starting with the lowest number first. The attributes of the physical path are compared to the path specification in the claim rule. If there is a match, the host assigns the MPP specified in the claim rule to manage the physical path. This continues until all physical paths are claimed by corresponding MPPs, either third-party multipathing plug-ins or the native multipathing plug-in (NMP).

For general information on multipathing plug-ins, see Managing Multiple Paths.

For the paths managed by the NMP module, a second set of claim rules is applied. These rules determine which Storage Array Type Plug-In (SATP) should be used to manage the paths for a specific array type, and which Path Selection Plug-In (PSP) is to be used for each storage device. For example, for a storage device that belongs to the EMC CLARiiON CX storage family and is not configured as ALUA device, the default SATP is VMW_SATP_CX and the default PSP is Most Recently Used.

Use the vSphere Client to view which SATP and PSP the host is using for a specific storage device and the status of all available paths for this storage device. If needed, you can change the default VMware PSP using the vSphere Client. To change the default SATP, you need to modify claim rules using the vSphere CLI.

For detailed descriptions of the commands available to manage PSA, see the vSphere Command-Line Interface Installation and Scripting Guide and the vSphere Command-Line Interface Reference.