Dell EMC PowerVault MD 34XX/38XX Series Storage Arrays Administrator's Guide

A preferred controller is a RAID controller module designated as the owner of a virtual disk or disk group. The preferred controller is automatically selected by the MD Storage Manager when a virtual disk is created. You can change the preferred RAID controller module owner of a virtual disk after it is created. If a host is connected to only one RAID controller module, the preferred owner must manually be assigned to the RAID controller module that the host can access.

Paths used by the preferred RAID controller module to access either the disks or the host server are called the preferred paths; redundant paths are called the alternate paths. If a failure causes the preferred path to become inaccessible, the storage array automatically uses the alternate path to access data, and the enclosure status LED blinks amber.