6.5.1

The policy is displayed in the client as the Most Recently Used (VMware)
path selection policy.
VMW_PSP_FIXED The host uses the designated preferred path, if it has been configured.
Otherwise, it selects the first working path discovered at system boot time.
If you want the host to use a particular preferred path, specify it manually.
Fixed is the default policy for most active-active storage devices.
Note If the host uses a default preferred path and the path's status turns
to Dead, a new path is selected as preferred. However, if you explicitly
designate the preferred path, it will remain preferred even when it becomes
inaccessible.
Displayed in the client as the Fixed (VMware) path selection policy.
VMW_PSP_RR The host uses an automatic path selection algorithm rotating through all
active paths when connecting to active-passive arrays, or through all
available paths when connecting to active-active arrays. RR is the default
for a number of arrays and can be used with both active-active and active-
passive arrays to implement load balancing across paths for different LUNs.
Displayed in the client as the Round Robin (VMware) path selection policy.
VMware NMP Flow of I/O
When a virtual machine issues an I/O request to a storage device managed by the NMP, the following
process takes place.
1 The NMP calls the PSP assigned to this storage device.
2 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 Claiming
When you start your ESXi host or rescan your storage adapter, the host discovers all physical paths to
storage devices available to the host. Based on a set of claim rules, the host determines which
multipathing plug-in (MPP) should claim the paths to a particular device and become responsible for
managing the multipathing support for the device.
By default, the host performs a periodic path evaluation every 5 minutes causing any unclaimed paths to
be claimed by the appropriate MPP.
vSphere Storage
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