Items to backup.
Im some what confused, When Choosing Items to backup, and selecting Disks/volumes the Iscsi disk appears for windows server backup.
Correct me If im wrong, but I dont see that its necessary to backup that iscsi target as it is on a seperate storage device.
However if i unselect the disk im told "For a single-pass backup, we recomend that you select the entire machine rather than its disks or volumes, otherwise application data may be backed up incompletely"
No checks about volumes' properties is performed to display this warning. Even if they do not contain application data the warning is displayed. It was done to prevent backup failures when user unintentionally select e.g. only system volume while data may be located on other volumes. In your case you can just ignore it.