Not all NAS provides iSCSI. Once it is connected, you need to partition and format before using. It works as local disk and cannot be resize easily.
It is a block level protocol.
Because I want to select the best solution to backup my files from Lenovo ThinkCentre Edge 72z 3574-U3V to QNAP TS-112, I prepare a test to collect data. I made a sample backup with one 3.3GB VDI file, 851 jpeg photos for 2.9GB, and 6 AVI video for 911.2MB. Lenovo ThinkCentre Edge 72z to QNAP TS-112 are connected directly via Gigabit Ethernet.