A cloud infrastructure architect is designing a new IaaS zone that will present block storage to hypervisor hosts over an IP-based iSCSI storage network. During testing, throughput to the storage array is far below the array's rated capacity, and packet captures show heavy TCP retransmissions and fragmentation on the storage VLAN, which shares the same physical switches and default MTU as general tenant traffic. Which design change should the architect prioritize to address the root cause?