The Number of NICs
With a separate shared directory mapped as a network drive on each of our three test servers, we dove into our Iometer performance tests. One of our challenges was to fairly compare the three systems that offer dual-Gigabit Ethernet NICs with the two that offer only a single port for storage. As a rule, we try to test all systems under identical circumstances, so we first tested both single- and dual-port systems in single-port mode, and systems with dual NICs were set to failover. In larger environments, when networked storage devices have dual NICs, they are often set to failover, so if one link to the storage is lost, another can take its place. The alternative to this is link aggregation or load balancing, which lets you combine two NICs for higher throughput. This feature is well-suited to smaller environments that don't necessarily require using the NICs in a redundant, failover mode and would instead opt for the higher performance of a load-balanced system.
Next we used the load-balancing feature, rather than link aggregation, because of its compatibility with most environments. Link aggregation requires switch-level support, and the increase in available bandwidth would be about the same in either of the dual-NIC modes. We also tested the fault-tolerance of the load-balancing setup by unplugging one of the links during testing. In all three cases, the performance immediately dipped to single-port speeds but, as expected, the connection to our servers was never completely interrupted.
We also tried reconnecting them during the test, but only the Snap Server and FlexNAS could reacquire the link and come back up to full speed; the AberNAS required a system restart to resynchronize the load-balanced connection. These results also confirmed that there is no good reason to limit the performance of dual-NIC systems by using them in failover mode, because load balancing offers reasonable fault tolerance for single-network environments.
With load balancing enabled, we were pleased to find that the performance of AberNAS 128 and the Snap Server 520 just about doubled: combined reads reached nearly 200 MBps and writes pushed 150 MBps. The Snap Server and FlexNAS systems made this process the easiest, letting us toggle between modes, but the WSS-based AberNAS forced us to drop to the OS to set up the NICs. PrimeArray's FlexNAS 6800E XT didn't really push the upper limits in our single-port tests in the first test, so enabling load balancing actually decreased its performance a tiny bit. Of the other two systems, only HP's ProLiant ML310 G3 came close to matching the single-port capabilities of the systems from Aberdeen and Adaptec. The low-priced Infrant ReadyNAS NV came in last.
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