vSphere Storage - ESXi 5.1 - Documentation - VMware

6 The SATP interprets the I/O command errors and, when appropriate, activates the inactive paths.
7 The PSP is called to select a new path on which to issue the I/O.
Path Scanning and Claiming
When you start your ESXi 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, 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 plugins
or the native multipathing plug-in (NMP).
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.
Use the vSphere Client or the vSphere Web 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 client. To change the default SATP, you need to modify claim rules using the vSphere
CLI.
You can find some information about modifying claim rules in “Managing Storage Paths and Multipathing
Plug-Ins,” on page 205.
For more information about the commands available to manage PSA, see Getting Started with vSphere Command-
Line Interfaces.
For a complete list of storage arrays and corresponding SATPs and PSPs, see the SAN Array Model Reference
section of the vSphere Compatibility Guide.
Viewing the Paths Information
You can review the storage array type policy (SATP) and path selection policy (PSP) that the ESXi host uses
for a specific storage device and the status of all available paths for this storage device. You can access the path
information from both the Datastores and Devices views. For datastores, you review the paths that connect to
the device the datastore is deployed on.
The path information includes the SATP assigned to manage the device, the PSP, a list of paths, and the status
of each path. The following path status information can appear:
Active Paths available for issuing I/O to a LUN. A single or multiple working paths
currently used for transferring data are marked as Active (I/O).
Standby If active paths fail, the path can quickly become operational and can be used
for I/O.
Disabled The path is disabled and no data can be transferred.
Chapter 20 Understanding Multipathing and Failover
Dead The software cannot connect to the disk through this path.
If you are using the Fixed path policy, you can see which path is the preferred path. The preferred path is
marked with an asterisk (*) in the Preferred column.
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