iSCSI is an IETF standard (RFC 3720) for remote access to block-level storage. It can be thought of as similar to NFS, except that an NFS server exports files; the iSCSI target exports blocks to the iSCSI initiators, which are the clients. To set up the target, you need to edit the /etc/iscsi/targets file. It has a certain layout, to provide a means of (a) mirroring and (b) combining multiple areas to present one large contiguous area of storage. This can be multiply-layered.