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

vSphere Storage6 Reboot guest OS for the change to take effect.Managing Multiple PathsTo manage storage multipathing, ESXi uses a collection of Storage APIs, also called the Pluggable StorageArchitecture (PSA). The PSA is an open, modular framework that coordinates the simultaneous operation ofmultiple multipathing plug-ins (MPPs). The PSA allows 3rd party software developers to design their ownload balancing techniques and failover mechanisms for particular storage array, and insert their codedirectly into the ESXi storage I/O path.Topics discussing path management use the following acronyms.Table 23‐1. Multipathing AcronymsAcronymPSANMPPSPSATPDefinitionPluggable Storage ArchitectureNative Multipathing Plug-In. Generic VMwaremultipathing module.Path Selection Plug-In, also called Path Selection Policy.Handles path selection for a given device.Storage Array Type Plug-In, also called Storage Array TypePolicy. Handles path failover for a given storage array.The VMkernel multipathing plug-in that ESXi provides by default is the VMware Native Multipathing Plug-In (NMP). The NMP is an extensible module that manages sub plug-ins. There are two types of NMP subplug-ins, Storage Array Type Plug-Ins (SATPs), and Path Selection Plug-Ins (PSPs). SATPs and PSPs can bebuilt-in and provided by VMware, or can be provided by a third party.If more multipathing functionality is required, a third party can also provide an MPP to run in addition to,or as a replacement for, the default NMP.When coordinating the VMware NMP and any installed third-party MPPs, the PSA performs the followingtasks:• Loads and unloads multipathing plug-ins.• Hides virtual machine specifics from a particular plug-in.• Routes I/O requests for a specific logical device to the MPP managing that device.• Handles I/O queueing to the logical devices.• Implements logical device bandwidth sharing between virtual machines.• Handles I/O queueing to the physical storage HBAs.• Handles physical path discovery and removal.• Provides logical device and physical path I/O statistics.As the Pluggable Storage Architecture illustration shows, multiple third-party MPPs can run in parallel withthe VMware NMP. When installed, the third-party MPPs replace the behavior of the NMP and takecomplete control of the path failover and the load-balancing operations for specified storage devices.220 VMware, Inc.