Storage Networking Architectures
Network Metrics
Mode of Operation
Half Duplex permits transmission in one direction at a time
Full duplex allows simultaneous transmission in both directions
Half Duplex
Half Duplex on 100Mb/s Ethernet
100Mb/s
Tx (Mb/s) Rx (Mb/s) TOTAL
100 0 100
No Traffic
0 100 100
iSCSI storage
or NAS
Full Duplex
Full Duplex on 100Mb/s Ethernet
Tx (Mb/s) Rx (Mb/s) TOTAL
100Mb/s
100 0 100
0 100 100
100Mb/s 100 100 200
iSCSI storage
or NAS
Fibre Channel is always full duplex.
10-Base-T and 100-Base-T Ethernet and Gigabit Ethernet are usually Full
Duplex, but can be misconfigured as Half Duplex on some devices.
Another issue which can occur with Ethernet is that the auto-negotiation
incorrectly negotiates the link speed to a lower speed link than the devices are
capable of. For example two Gigabit Ethernet devices could possibly connect
together as 100-Base-T (100Mb/s) instead of Gigabit Ethernet (1000Mb/s).
This was a common problem in the early days of Ethernet but is less of an
issue today. Some vendors will still recommend setting ports to fixed-speed
rather than auto-negotiate, to ensure the links do come up at the right speed.