A continuación descubrimos el pool de almacenamiento, como se listan los LUNS y se ven detalles.

[root@haya1 ~]# virsh pool-list --all
Name                 State      Autostart
-----------------------------------------
abedul_iscsi         active     yes
abedul_pruebas       active     yes
default              active     yes


#Encontrar las lun disponibles:

[root@haya1 ~]#  virsh vol-list abedul_iscsi
Name                 Path
-----------------------------------------
unit:0:0:1           /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-1
unit:0:0:10          /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-10
unit:0:0:11          /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-11
unit:0:0:12          /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-12
unit:0:0:13          /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-13
unit:0:0:14          /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-14
unit:0:0:15          /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-15
unit:0:0:2         /ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-2
unit:0:0:20          /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-20
unit:0:0:21          /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-21
unit:0:0:3           /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-3
unit:0:0:4           /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-4
unit:0:0:5           /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-5
unit:0:0:6           /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-6
unit:0:0:9           /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-9

#
[root@haya1 ~]# virsh vol-info /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-6
Name:           unit:0:0:6
Type:           block
Capacity:       50.00 GiB
Allocation:     50.00 GiB
#

[root@haya1 ~]# virsh vol-dumpxml  /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-6
<volume>
  <name>unit:0:0:6</name>
  <key>1IET_00010006</key>
  <source>
  </source>
  <capacity unit='bytes'>53687091200</capacity>
  <allocation unit='bytes'>53687091200</allocation>
  <target>
    <path>/dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-6</path>
    <format type='unknown'/>
    <permissions>
      <mode>0660</mode>
      <owner>0</owner>
      <group>0</group>
    </permissions>
    <timestamps>
      <atime>1495200423.370916984</atime>
      <mtime>1495200422.018916984</mtime>
      <ctime>1495200422.229916984</ctime>
    </timestamps>
  </target>
</volume>

Lo primero se crea la MV, creo que al poner --os-variant=rhel6 ya no es necesario indicar explicitamente que use los drives paravirtualizados virtio.

virt-install \
--name spock2 \
--ram=3072 \
--disk /dev/disk/by-path/ip-192.168.202.249:3260-iscsi-iqn.2012-03.es.unican:abedul.kvm-lun-6,bus=virtio \
--cdrom /root/CentOS-6.9-x86_64-minimal.iso \
--network bridge=br1 \
--network bridge=br2 \
--os-type=linux \
--os-variant=rhel6 \
--graphics vnc \

A partir de aqui desde la consola de virt-manager continuamos con la instalacion del SO. (Teclado ES, quitar LVG, y dejamos solo dos particiones /dev/vda1 y /dev/vda2 ( / y swap ) )