6.0.1

After the NMP determines which SATP to use for a specic storage device and associates the SATP with the
physical paths for that storage device, the SATP implements the tasks that include the following:
n
Monitors the health of each physical path.
n
Reports changes in the state of each physical path.
n
Performs array-specic actions necessary for storage fail-over. For example, for active-passive devices, it
can activate passive paths.
VMware PSPs
Path Selection Plug-Ins (PSPs) are sub plug-ins of the VMware NMP and are responsible for choosing a
physical path for I/O requests.
The VMware NMP assigns a default PSP for each logical device based on the SATP associated with the
physical paths for that device. You can override the default PSP. For information, see “Path Scanning and
Claiming,” on page 191.
By default, the VMware NMP supports the following PSPs:
VMW_PSP_MRU
The host selects the path that it used most recently. When the path becomes
unavailable, the host selects an alternative path. The host does not revert
back to the original path when that path becomes available again. There is no
preferred path seing with the MRU policy. MRU is the default policy for
most active-passive storage devices.
The VMW_PSP_MRU ranking capability allows you to assign ranks to
individual paths. To set ranks to individual paths, use the esxcli storage
nmp psp generic pathconfig set command. For details, see the VMware
knowledge base article at hp://kb.vmware.com/kb/2003468.
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 congured.
Otherwise, it selects the rst 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.
N 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 dierent 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.
vSphere Storage
190 VMware, Inc.