In this post I am going to create an active/active high-availability iSCSI cluster using CentOS 7, pacemaker, corosync, pcs/pcsd, and DRBD. I am not going to cover what each of these components do as I covered that in my previous article CentOS 7 active/passive Apache Cluster - Part 1 but I would recommend giving it a read. I also want to mention that this setup is based on a technical publication found on the Linbit site, the makers of DRBD, at http://www.linbit.com/en/resources/technical-publications/. There is additional information in that document as well as other technical publications that are well worth reading so I suggest everyone sign up and have a look at them by heading over to the Linbit site. I am putting my own spin on the instructions plus I am using the pcs shell instead of crm since it is now used in RHEL/CentOS 7.