EMC’s best practice for creating storage pools and RAID groups on mid to low end storage arrays (e.g. CLARiiON or VNX) has always been to create them using disks from a single Drive Array Enclosure (DAE). This configuration is sometimes referred to as horizontal striping. You may be wondering why this was the case as a complete DAE failure would result in data unavailablity for all pools/groups on the DAE. As such, you may be tempted to create pools/groups across multiple DAEs, which is sometimes referred to as vertical striping. To understand the reasons you need to first understand the physical configuration of EMC mid to low end storage arrays and then some DAE failure scenarios.