7
NETWORK DESIGN CONSIDERATIONS
EMC Isilon scale-out NAS clients demanding the highest possible 10 gigabit Ethernet performance use two physically isolated
networks, as shown below in the example in Figure 3.
Figure 3. Dual homed network for Jumbo Frames Support
The primary network in this design is a standard gigabit Ethernet network, shown at the bottom of figure 1. The gigabit Ethernet
network is common to all devices on the LAN using each device’s on-board gigabit Ethernet port(s). All devices on the gigabit LAN
segment utilize a standard Maximum Transmission Unit (MTU) of 1500 bytes per packet. The gigabit Ethernet network is a layer 3
network and each host on the network is configured with a default gateway address. Clients on this network with ATTO Technology
FastFrame NS 10 gigabit Ethernet network adapters installed are configured for a dual-homed network configuration. The 10 gigabit
Ethernet network shown at the top of figure 1 is common to only 10 gigabit enabled clients.
Unlike the gigabit Ethernet network, the 10 gigabit Ethernet network is a layer 2 Ethernet switch configured to pass jumbo frames or
packets with an MTU size of 9000. Each host interface on the 10 gigabit Ethernet network is configured with an MTU of 9000. The
10 gigabit switch supporting this network is configured with an MTU of 9216 bytes in order to prevent the re-transmission of packets
exceeding 9000 bytes. Every client on the 10 gigabit LAN and every EMC Isilon 10 gigabit Ethernet interface is configured with an
MTU of exactly 9000 bytes per packet in order to prevent re-transmission of packets due to fragmentation.
EMC Isilon scale-out NAS clients utilizing a jumbo frame enabled LAN segment keep all interfaces using an MTU of 9000 bytes per
packet isolated to a dedicated jumbo frames network. The only interface that is allowed to route traffic to other subnets is the
gigabit Ethernet interface configured with an MTU of 1500 bytes per packet. The MTU 1500 interface is also configured as the
primary interface on each of the client operating systems. A “jumbo frames” enabled 10 gigabit Ethernet network may improve
workflow performance by more efficiently packetizing data for network file transfers.
EMC Isilon scale-out NAS customers wishing to simplify their network infrastructure configure their 10 gigabit Ethernet switches in a
layer 3/4 topology with an MTU of 1500 bytes per packet. While increasing MTU may yield a worthwhile performance increase in
some environments, the added complexity of dual-homing each client may negate the benefits of simplicity in a NAS architecture.
Careful consideration must be taken before enabling jumbo frame sizes, as MTU sizes must never be mixed on the same network
segment.
For optimal performance, 10 gigabit Ethernet clients are connected to the same switch as the EMC Isilon 10 gigabit Ethernet
connections, as each “hop” on a network of tiered Ethernet switches adds latency to file transfers.
PERFORMANCE
When validating performance for a 10 GbE enabled client, it is important to first set a baseline to determine if your performance is
being limited by a physical network or driver issue. To validate you will be able to saturate a network connection, make sure you run
an iperf test to read from each client network interface to each Isilon node network interface and write from each client network
interface to each Isilon node network interface. Iperf an open source tool for performing network performance measurement. Iperf
is pre-installed on every Isilon cluster. Windows binaries Linux install packages for iperf are available at http://iperf.sourceforge.net.
To install iperf on Mac OS X, first install the Brew package manager from the Mac OS X command line interface:
ruby -e "$(curl -fsSL
https://raw.githubusercontent.com/Homebrew/install/master/install
