TonyJK,  I'd like to direct your attention to the bottom of the post though (things change of course).  It was responding to someone running a CX3 but still relates to you; important (from a support perspective) is the comment in bold.  [...] Also, you have correctly identified that the CX3 while it supports ALUA which was introduced with FLARE 26, integration with ESX/ESXi 4.x+ requires SCSI-3 reservation support which was introduced in a later revision; FLARE 26 only supports SCSI-2 reservations.  In the original post above, it was mentioned while technically FLARE 04.28.000.5.704+ provides that mechanism (both SCSI-2 and SCSI-3 reservations) and was the minimum supported at the time, recently "E-Lab and VMware jointly made the decision to support only ALUA on FLARE R30 and VNX OE for Block" **. [...]   This is noted in the following KB article:  emc99467: ""What are the Initiator, Arraycommpath, and Failovermode settings for PowerPath, DMP, PVLinks, and native failover software?   Therefore, technically at FLARE 29, you should be running failover mode of 1 (passive-not-ready) and your choices for the path selection policy would be either:  1) MRU 2) Round-Robin  emc301503: "What are the recommended path failover policies for VMware ESX/ESXi NMP (native multipath plugin) ?"  For Active/Active and ALUA enabled storage arrays, fixed is the default policy.RoundRobin is supported and can be a good option to improve performance.  For Active/Passive arrays MRU is the recommended policy. RoundRobin is supported and can be used to improve performance.   However, at failover mode of 1, Fixed is not recommended as it can cause path thrashing:  [...] 2) Host Connectivity Guide for VMware ESX Server (search support.emc.com)  "For VNX series and CLARiiON systems not capable of ALUAfailover mode support, the MRU or Round Robin policies arerecommended to avoid path thrashing." [...] 
Hi,  We just enabl ALUA on a CX4-240 Storage Array (FLARE 29).  We would like to know which PSP Plugin should be used ?  Round Robin or Fixed ?  There is a compatbility guide in VMware but it is for FLARE 30 only.  Just wonder whether there is a similar one in EMC Support Document with previous FLARE version.  Thanks
VMware PSP Plugin for ALUA SAN (FLARE 29) ?