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.

In this post I’m going to take a look at a two-node CentOS 7 Apache active/passive cluster using mostly packages in the Red Hat cluster suite.  In case you don’t already know, CentOS is created by making use of the source packages provided by Red Hat Enterprise Linux (RHEL). 

In my last post, I went through the steps to build an active/passive Apache web hosting cluster on CentOS 7.  Building on the same platform, I’m going to add replicated block storage to our cluster by utilizing DRBD. 

If you have been following along, in my last two posts we successfully set up an active/passive Apache cluster on CentOS 7 and then we added shared storage. The storage I chose was local storage. In this post, I'll be replacing that with iSCSI shared storage and adding MySQL (actually MariaDB).

In this post, I am going to resize both DRBD resources created in my last post titled CentOS 7 Active/Active iSCSI Cluster with no down-time.  In fact, I will have 2 virtual mahines running, one per DRBD resource, while I make this change.  The primary consideration is that the backing device must have the ability to grow online (think LVM).  I'm using virtual machines so I will be able to enlarge the resources at the hypervisor level.  A lot of the information in this post comes from the DRBD site http://www.drbd.org/en/doc/users-guide-83/s-resizing.  I am just adding a few steps along the way and including some screen captures.