No more NIC-bottleneck blues
Redundancy permeates every nook and cranny of the computer industry, and new technologies increase fault tolerance and accommodate 24 X 7 availability. At the same time, processor speed and memory size continue to increase at a blinding rate. Despite these innovations, the network interface card (NIC--i.e., the physical network adapter) remains a weak link for many servers. The NIC often throttles performance and acts as a point of failure.
You can install a second NIC in the server to help alleviate these problems. However, this configuration is less than ideal because you must place each NIC in that system on a separate subnet. As a result, you must fragment your network to accommodate your server's NICs.
What if you combine two or more NICs to create a high-speed virtual NIC that you access from one subnet? In this month's review, I'll focus on three software-based solutions that combine multiple LAN connections (i.e., ports) in one system to create a high-performance data pipe that provides output two to four times faster than systems with one LAN connection. These super NIC arrays accomplish this increased speed by directing output through any available NIC port. In all three products, a network device interface specification (NDIS) driver balances the load of the multiple LAN connections.
The benefits of using super NIC technology include increased throughput performance and stable load balancing of requests and the subsequent output. Super NICs also provide fault tolerance, so if one LAN connection fails, the system removes that connection from the NIC array and dynamically balances the load among the remaining connections. When the failed connection comes back online, it dynamically rejoins the NIC array.
The Test Environment
I tested all three software packages using a brand-name server with four 200MHz Pentium Pro processors, 2GB of RAM, 512KB of Level 2 cache, and two 4.2GB hard disks. I configured the test server with an Adaptec ANA-6944A/TX quad-port NIC that uses only one PCI slot but provides four separate LAN connections.
Next, I set up four 166MHz Pentium client systems each with an Adaptec 10/100 NIC and at least 64MB of RAM. I created a workgroup running TCP/IP and attached the four workstations and the test server to a Compaq NetIntelligent switch.
Before testing each product, I installed Windows NT Server, Enterprise Edition (NTS/E), Service Pack 3 (SP3), and the Microsoft NDIS hotfix on each system. This hotfix is a post-SP3 patch that corrects a memory leak in Microsoft's NDIS driver that can result in a blue screen of death. This memory leak often occurs when you use intermediate (layered) NDIS miniport drivers under NT Server. The layered drivers typically provide additional functionality, such as the virtual NIC feature in the products I reviewed for this article. You can download the free NDIS hotfix for Intel and Alpha systems from Microsoft's FTP site (ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40/hotfixes-postSP3/ndis-fix).
Until Service Pack 4 (SP4) arrives, I recommend applying the NDIS hotfix each time you apply SP3, even if you aren't loading an intermediate driver. Averting the blue screen of death is worth the extra time you spend installing the fix.
The Tests
To test the three NIC load-balancing products, I evaluated several criteria, as Table 1, page 74, shows. Specifically, I considered each product's price and which NICs you can use with each product. I identified which protocols and which operating systems (OSs) each product supports. I looked at each product's ability to automatically remove a failed LAN connection from the NIC array and automatically rejoin an operational LAN connection to the NIC array. I identified which products support segmenting a virtual NIC into two or more separate LAN connections (segmenting lets you achieve greater throughput and fault tolerance for various departments or users within an organization). I also evaluated whether each product includes a built-in monitoring tool and whether each product includes built-in alert options, such as email, Simple Network Management Protocol (SNMP) messaging, or paging. Finally, I considered each product's installation and configuration process, documentation, and technical support.
After I evaluated each product's features, I used the Web Capacity Analysis Tool (WCAT) that comes with Microsoft Windows Internet Information Server Resource Kit to test the products. WCAT runs scripts that generate various workloads from client servers to a specific server. I used the four client systems to run the workload against the 4-way server running the NIC load-balancing products. Each client simulated 250 simultaneous user streams. I ran two baseline tests and then ran the same test to measure each product's ability to balance the workload.
To measure the I/O, I installed Network General's NetXray on a separate system. NetXray showed data transfer per second for each NIC via its unique media access control (MAC) address and by IP address. Finally, I used Artisoft's ConfigSafe 1.0 after each test to restore the system settings to the original configuration, and ran a batch file to clear the system cache so that the cached data didn't skew the test results.