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This chapter is from the book

Anatomy of PSA Components

Figure 5.8 is a block diagram showing the components of PSA framework.

Figure 5.8

Figure 5.8. NMP components of PSA framework

Now that we covered the individual components of PSA framework, let’s put its pieces together. Figure 5.8 shows the NMP component of the PSA framework. NMP provides facilities for configuration, general device management, array-specific management, and path selection policies.

The configuration of NMP-related components can be done via ESXCLI or the user interface (UI) provided by vSphere Client. Read more on this topic in the “Modifying PSA Plug-in Configurations Using the UI” section later in this chapter.

Multipathing and failover policy is set by NMP with the aid of PSPs. For details on how to configure the PSP for a given array, see the “Modifying PSA Plug-in Configurations Using the UI” section later in this chapter.

Arrray-specific functions are handled by NMP via the following functions:

  • Identification—This is done by interpreting the response data to various inquiry commands (Standard Inquiry and Vital Product Data (VPD) received from the array/storage. This provides details of device identification which include the following:
    • Vendor
    • Model
    • LUN number
    • Device ID—for example, NAA ID, serial number
    • Supported mode pages—for example, page 80 or 83

    I cover more detail and examples of inquiry strings in Chapter 7, “Multipathing and Failover” in, the “LUN Discovery and Path Enumeration” section.

  • Error Codes—NMP interprets error codes received from the storage arrays with help from the corresponding SATPs and acts upon these errors. For example, an SATP can identify a path as dead.
  • Failover—After NMP interprets the error codes, it reacts in response to them. Continuing with the example, after a path is identified as dead, NMP instructs the relevant SATP to activate standby paths and then instructs the relevant PSP to issue the I/O on one of the activated paths. In this example, there are no active paths remaining, which results in activating standby paths (which is the case for Active/Passive arrays).
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