Information Technology Reference
In-Depth Information
major VMware releases. With the PSA's modular architecture, vSphere administrators have a
much more l exible approach.
Four different modules compose the PSA:
Native multipathing plug-in (NMP)
Storage array type plug-in (SATP)
Path selection plug-in (PSP)
Multipathing plug-in (MPP)
Any given ESXi host can have multiple modules in use at any point and can be connected to
multiple arrays, and you can coni gure the combination of modules used (an NMP/SATP/PSP
combination or an MPP) on a LUN-by-LUN basis.
Let's see how they work together.
Understanding the NMP Module
The NMP module handles overall MPIO (multipath I/O) behavior and array identii cation. The
NMP leverages the SATP and PSP modules and isn't generally coni gured in any way.
Understanding SATP Modules
SATP modules handle path failover for a given storage array and determine the failover type for
a LUN.
vSphere ships with SATPs for a broad set of arrays, with generic SATPs for nonspecii ed
arrays and a local SATP for local storage. The SATP modules contain the rules on how to handle
array-specii c actions or behavior as well as any specii c operations needed to manage array
paths. This is part of what makes the NMP modular (unlike the NMP in prior versions); it
doesn't need to contain the array-specii c logic, and additional modules for new arrays can be
added without changing the NMP. Using the SCSI Array ID reported by the array via a SCSI
query, the NMP selects the appropriate SATP to use. After that, the SATP monitors, deactivates,
and activates paths (and when a manual rescan occurs, detects new paths)—providing infor-
mation up to the NMP. The SATP also performs array-specii c tasks such as activating passive
paths on active-passive arrays.
To see what array SATP modules exist, enter the following command from the vCLI (we ran
this from the ESXi shell):
esxcli storage nmp satp list
Figure 6.19 shows the results this command returns (note that the default PSP for a given
SATP is also shown).
Understanding PSP Modules
The PSP module handles the actual path used for every given I/O.
The NMP assigns a default PSP, which can be overridden manually for every LUN based on
the SATP associated with that device. This command (and the output captured in Figure 6.20)
shows you the three PSPs vSphere includes by default:
esxcli storage nmp psp list
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