6.0.1

2 The PSP selects an appropriate physical path on which to issue the I/O.
3 The NMP issues the I/O request on the path selected by the PSP.
4 If the I/O operation is successful, the NMP reports its completion.
5 If the I/O operation reports an error, the NMP calls the appropriate SATP.
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 rst. The aributes of the physical path are compared to the path specication in the
claim rule. If there is a match, the host assigns the MPP specied 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 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 specic array type, and
which Path Selection Plug-In (PSP) is to be used for each storage device.
Use the vSphere Web Client to view which SATP and PSP the host is using for a specic 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 nd some information about modifying claim rules in “Managing Storage Paths and Multipathing
Plug-Ins,” on page 194.
For more information about the commands available to manage PSA, see Geing 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 specic 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.
Chapter 17 Understanding Multipathing and Failover
VMware, Inc. 191