Note: No Storage APIs for MultiPathing Support in this edition
Uses natively integrated multi-path capability or can take advantage of vendor specific capabilities using vStorage APIs for Multipathing. By default, ESXi provides an extensible multipathing module called the Native Multipathing Plug-In (NMP). Generally, the VMware NMP supports all storage arrays listed on the VMware storage HCL and provides a default path selection algorithm based on the array type. The NMP associates a set of physical paths with a specific storage device, or LUN. The specific details of handling path failover for a given storage array are delegated to a Storage Array Type Plug-In (SATP). The specific details for determining which physical path is used to issue an I/O request to a storage device are handled by a Path Selection Plug-In (PSP). SATPs and PSPs are sub plug-ins within the NMP module. With ESXi, the appropriate SATP for an array you use will be installed automatically. You do not need to obtain or download any SATPs.
vSphere 5.1 aims to improve All Paths Down (APD) and Permanent Device Loss (PDL) through the ability to handle more complex transient APD conditions. It does not allow hostd to become hung indefinitely when devices are removed in an uncontrolled manner.
• Enable VMware vSphere High Availability (vSphere HA) to detect PDL and be able to restart virtual machines
on other hosts in the cluster that might not have this PDL state on the datastore.
• Introduce a PDL method for those iSCSI arrays that present only one LUN for each target. These arrays were
problematic, because after LUN access was lost, the target also was lost. Therefore, the ESXi host had no way
of reclaiming any SCSI sense codes.