vSphere Storage - ESXi 5.1 - Documentation - VMware

vSphere Storage
6 Reboot guest OS for the change to take effect.
Managing Multiple Paths
To manage storage multipathing, ESXi uses a collection of Storage APIs, also called the Pluggable Storage
Architecture (PSA). The PSA is an open, modular framework that coordinates the simultaneous operation of
multiple multipathing plug-ins (MPPs). The PSA allows 3rd party software developers to design their own
load balancing techniques and failover mechanisms for particular storage array, and insert their code directly
into the ESXi storage I/O path.
Topics discussing path management use the following acronyms.
Table 20-1. Multipathing Acronyms
Acronym Definition
PSA Pluggable Storage Architecture
NMP Native Multipathing Plug-In. Generic VMware multipathing
module.
PSP Path Selection Plug-In, also called Path Selection Policy.
Handles path selection for a given device.
SATP Storage Array Type Plug-In, also called Storage Array Type
Policy. 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 sub plugins,
Storage Array Type Plug-Ins (SATPs), and Path Selection Plug-Ins (PSPs). SATPs and PSPs can be built-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 following
tasks:
n Loads and unloads multipathing plug-ins.
n Hides virtual machine specifics from a particular plug-in.
n Routes I/O requests for a specific logical device to the MPP managing that device.
n Handles I/O queueing to the logical devices.
n Implements logical device bandwidth sharing between virtual machines.
n Handles I/O queueing to the physical storage HBAs.
n Handles physical path discovery and removal.
n Provides logical device and physical path I/O statistics.
As the Pluggable Storage Architecture illustration shows, multiple third-party MPPs can run in parallel with
the VMware NMP. When installed, the third-party MPPs replace the behavior of the NMP and take complete
control of the path failover and the load-balancing operations for specified storage devices.
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