Previously, Red Hat Virtualization only allowed hostdev passthrough of USB and PCI devices. To assign storage cards directly to a virtual machine users had to assign the whole adapter as PCI device. The problem with this approach is that PCI passthrough has specific hardware requirements.
This feature allows administrators to passthrough a LUN directly to a virtual machine, allowing for full set of SG commands. This means tapes, changers, and anything speaking SCSI protocol can be assigned directly without specific hardware requirements with the exception of assigned device itself.