vsphere-esxi-vcenter-server-55-storage-guide

Chapter 23 Understanding Multipathing and Failover2 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 ClaimingWhen you start your ESXi host or rescan your storage adapter, the host discovers all physical paths tostorage devices available to the host. Based on a set of claim rules, the host determines which multipathingplug-in (MPP) should claim the paths to a particular device and become responsible for managing themultipathing support for the device.By default, the host performs a periodic path evaluation every 5 minutes causing any unclaimed paths to beclaimed by the appropriate MPP.The claim rules are numbered. For each physical path, the host runs through the claim rules starting withthe lowest number first. The attributes of the physical path are compared to the path specification in theclaim rule. If there is a match, the host assigns the MPP specified in the claim rule to manage the physicalpath. This continues until all physical paths are claimed by corresponding MPPs, either third-partymultipathing 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 determinewhich Storage Array Type Plug-In (SATP) should be used to manage the paths for a specific array type, andwhich 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 specific storage device andthe status of all available paths for this storage device. If needed, you can change the default VMware PSPusing 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 MultipathingPlug-Ins,” on page 226.For more information about the commands available to manage PSA, see Getting Started with vSphereCommand-Line Interfaces.For a complete list of storage arrays and corresponding SATPs and PSPs, see the SAN Array ModelReference section of the vSphere Compatibility Guide.Viewing the Paths InformationYou can review the storage array type policy (SATP) and path selection policy (PSP) that the ESXi host usesfor a specific storage device and the status of all available paths for this storage device. You can access thepath information from both the Datastores and Devices views. For datastores, you review the paths thatconnect 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 thestatus of each path. The following path status information can appear:ActiveStandbyPaths available for issuing I/O to a LUN. A single or multiple working pathscurrently used for transferring data are marked as Active (I/O).If active paths fail, the path can quickly become operational and can be usedfor I/O.VMware, Inc. 223