Sure, Jumbo Frames are a great Feature - but definitely not indispensable for using iSCSI.
There is no Performance Issue with iSCSI. iSCSI or NAS works well - only the
Replication ist very Slow 400 - 800 KByte/Sec.

But I will also try JF with 9000 Byte on the Replication Interface.

Thx for the Information!!