6.7

Each PSP enables and enforces a corresponding path selection policy.
VMW_PSP_MRU —
Most Recently Used
(VMware)
The Most Recently Used (VMware) policy is enforced by VMW_PSP_MRU.
It selects the first working path discovered at system boot time. When the
path becomes unavailable, the host selects an alternative path. The host
does not revert to the original path when that path becomes available. The
Most Recently Used policy does not use the preferred path setting. This
policy is default for most active-passive storage devices.
The VMW_PSP_MRU supports path ranking. 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
http://kb.vmware.com/kb/2003468 and the vSphere Command-Line
Interface Reference documentation.
VMW_PSP_FIXED —
Fixed (VMware)
This Fixed (VMware) policy is implemented by VMW_PSP_FIXED. The
policy uses the designated preferred path. If the preferred path is not
assigned, the policy selects the first working path discovered at system
boot time. If the preferred path becomes unavailable, the host selects an
alternative available path. The host returns to the previously defined
preferred path when it becomes available again.
Fixed is the default policy for most active-active storage devices.
VMW_PSP_RR —
Round Robin (VMware)
VMW_PSP_RR enables the Round Robin (VMware) policy. The policy uses
an automatic path selection algorithm rotating through the configured paths.
Round Robin is the default policy for many arrays. The policy can be used
with both active-active and active-passive arrays to implement load
balancing across paths for different LUNs. With active-passive arrays, the
policy uses all active paths. With active-active arrays, the policy uses all
available paths.
VMW_PSP_RR has configurable options that you can modify on the
command line. To set these parameters, use the esxcli storage nmp
psp roundrobin command. For details, see the vSphere Command-Line
Interface Reference documentation.
VMware SATPs
Storage Array Type Plug-ins (SATPs) are responsible for array-specific operations. The SATPs are
submodules of the VMware NMP.
ESXi offers an SATP for every type of array that VMware supports. ESXi also provides default SATPs that
support non-specific active-active, active-passive, ALUA, and local devices.
Each SATP accommodates special characteristics of a certain class of storage arrays. The SATP can
perform the array-specific operations required to detect path state and to activate an inactive path. As a
result, the NMP module itself can work with multiple storage arrays without having to be aware of the
storage device specifics.
vSphere Storage
VMware, Inc. 212