Need help to under stand storage configuration

I am doing a test lab for RHEV.
I have a VMware esxi host, in which it has two RHEVH6.5 hosts as VM's and one RHEVM in third VM. I have installed open filer in fourth VM for ISCSI storage.

I have added both host to default cluster and created a new iscsi storage domain which is connected by host1. I am able to create and install a VM. I am able to migrate the VM from one host to another.

The issue I am facing is that, if the host1 is down, than immediately ISCSI storage domain became offline. How a VM and storage can be highly available.
What type of storage file system is used in RHEV cluster.