You can increase the size of iSCSI disks too.  Go to Storage > Generic iSCSI Storage > Generic Storage Details > Click on the Virtual Disks tab.  You can either add a separate virtual disk or extend the capacity of the existing virtual disk (click on the details button after highlighting the virtual disk and go to Vistual Disk Capacity tab).
I noticed that when you create a generic iSCSI volume you cannot increase the size at a later date. You can however do this if you create a VMware volume. Why is this and is there any way with the CLI to increase a generic iSCSI volume
Increasing iSCSI volume size