When coordinating the VM NMP and any installed 3-party MPP, what operations does the PSA perform?
Implements logical devices bandwidth sharing
Process I/O request to logical devices
Associate physical path with logical devices
Manage physical path claiming and unclaiming
it is ,,Implements logical devices bandwidth sharing", as the other alternatives are performed by NMP. For reference please refer to page 23-24 of this document http:// www.vmware.com/pdf/vsphere4/r40/vsp_40_san_cfg.pdf
What does PSA do?
It coordinates the simultaneous operation of multiple multipathing plug-ins (MPPs). Yes that means you could have multiple and different plug-ins installed. But so far only EMC came with MPP plug-in called PowerPath/VE. By the way did you know that you can use EMC PowerPath/VE to provide multipathing and load balancing path management to EMC storage devices but also to any other storage vendors.
When coordinating the VMware NMP and any installed third-party MPPs, the PSA performs the following tasks
Loads and unloads multipathing plug-ins.
Hides virtual machine specifics from a particular plug-in.
Routes I/O requests for a specific logical device to the MPP managing that device.
Handles I/O queuing to the logical devices.
Implements logical device bandwidth sharing between virtual machines. (A)
Handles I/O queueing to the physical storage HBAs.
Handles physical path discovery and removal.
Provides logical device and physical path I/O statistics.