Many enterprises are upgrading networks to gigabit speeds and adding gigahertz processors to servers without giving the NIC any thought. Server performance bottlenecks involve more than the network and the processor. Host-system protocol processing is CPU intensive and can severely diminish your network and server upgrades. Typical protocol processing requires CPU time and dramatically affects read and write requests to buffers and Layer 2 cache. This generates lots of interrupts and can degrade a CPU's availability for other applications.

Enter SLIC technology, which off-loads TCP/IP protocol processing from the host system's CPU to silicon on the adapter. The 1000x1 contains an IPP (Internet Protocol Processor), a programmable ASIC optimized for protocol processing. The IPP engages protocol processing in hardware on the adapter and writes the frame directly to its final destination in main memory. This frees Layer 2 cache for other application processing and reduces the number of CPU interrupts over a PCI bus. By off-loading the protocol processing, the CPU is free to handle other application processing needs.

Testing

Alacritech sent us dual Intel Pentium III processors (1,266 MHz) with 512 MB of RAM in a slim 1U case. The system supported Microsoft Windows 2000 Server SP2 and contained two 1000x1 adapters that fit into two 64-bit, 66-MHz PCI slots. The Alacritech server also had two on-board Intel 8255x-based PCI Ethernet adapters. A single RJ-45 connector supports IEEE autonegotiation for 10Base-T, 100Base-TX and 1000Base-T operation. LEDs illuminate on the bracket to indicate the effective link state (10, 100 or 1,000 Mbps).

Performance Results Click here to enlarge

I replaced one of the 1000x1 adapters with a 3Com 10/100/1000 PCI-X Server NIC 3C996-T that did not use SLIC technology, and I installed the most recent Broadcom driver, version 1.29.00. For the 1000x1, I installed version 5.7 of Alacritech's driver. Windows did not find a Microsoft digital signature for the drivers and therefore would not guarantee that the drivers would work correctly under Windows, but I went ahead and successfully installed the new drivers without incident. Alacritech develops drivers for Microsoft Windows NT (SP 6A and above), Windows 2000 and Red Hat Linux. There is also a driver development kit for other operating systems.

I plugged both adapters into an Extreme Networks Summit7i switch. The Summit7i connected the server with the adapters under test to six Dell Computer Corp. 2550s running Windows 2000 Server SP2. The Dell servers sported dual Pentium III (1,000-MHz) processors and Broadcom Gigabit Ethernet controllers (driver version 1.29.00). All servers used NetIQ's Chariot Endpoint software 4.3 to generate test traffic.

I generated and analyzed traffic with Chariot 4.2. Chariot scripts simulated a server sending and receiving files in 4-, 16-, 64- and 256-KB increments. Three different scenarios were tested against each adapter while the other was disabled. In the first scenario, the Alacritech server sent files to the six Dell 2550s generating separate tests for each file size. In a second scenario, the six Dell servers sent the Alacritech server files in 4-, 16-, 64- and 256-KB increments. In a final scenario, I combined the two tests to simulate bidirectional traffic flowing to and from the servers simultaneously. I ran separate tests for each file size and added a 1-MB file transfer for good measure. Each test was run twice to verify and average the results (see chart above).

Speedy Info Transfer

The 1000x1 and the 3C996-T were neck and neck in separate tests used to send and receive 64- and 256-KB files. These results should compare well with those of most Gigabit Ethernet adapters. But the 1000x1 outperformed the 3C996-T--and wowed me--in sending and receiving smaller 4- and 16-KB files (smaller files use more server resources in processing a larger number of frames and transactions than larger files). When I combined the send and receive tests to generate bidirectional traffic, the 1000x1 really shined.

The 1000x1 bested the 3C996-T in each of the real-world, bidirectional tests. In traffic simulating 4-KB file transfers in both directions, the 1000x1 provided 514-Mbps throughput compared with the 3C996-T's 281 Mbps. In bidirectional tests with larger files (64/256 KB and 1 MB), the 1000x1 garnered greater than 1,700-Mbps throughput while the 3C996-T peaked at 982 Mbps. The real benefit, however, is in the 1000x1's protocol off-loads from the CPU.

Unlike other application-specific peripheral devices that off-load CPU cycles, such as SCSI adapters and graphic accelerator cards, SLIC technology is not a full off-load solution. The data control and exception (error) handling remain in software on the host system, which provides a central point of control. The hardware performs data-movement tasks including segmentation, reassembly and acknowledgement processing. Compare that with the capabilities of standard gigabit NICs, which essentially includes some check-sum calculation and perhaps the ability to perform TCP send segmentation.

The bidirectional tests with large file sizes taxed the host CPU using the 3C996-T adapter to 98 percent utilization. The same tests using the 1000x1 resulted in approximately 80 percent to 85 percent CPU utilization. The 1000x1 provided faster throughput and reduced CPU utilization across all my tests. This resulted in a P/E (performance/efficiency) ratio of 18.61 for the 1000x1 compared with a P/E ratio of 9.35 for the 3C996-T.

Vendor Information Alacritech 1000x1 Single Port Server and Storage Accelerator, $999. Available: April. Alacritech, (877) 533-7542, (408) 287-9997; fax (408) 436-0114. www.alacritech.com

After completing the tests with the 3C996-T, I removed it and returned the second 1000x1 to the Alacritech server. I teamed the two 1000x1 adapters together using Alacritech's SLIC team configuration tool and shared their corresponding ports as a group on the Summit7i switch. Both link aggregation and failover (IEEE 802.3ad) worked without a hitch. I did not test the 1000x1's support for iSCSI. When a standard is implemented consistently in host systems (initiators) and storage devices (targets), we'll see how well SLIC technology can deliver storage over IP.

Alacritech's sticker price is well above standard gigabit NICs, which typically run less than $200. But SLIC technology provides fast throughput while reducing host-server utilization, and it supports iSCSI. When you upgrade to gigabit networking and gigahertz servers, give the NIC some respect and check out Alacritech's 1000x1 adapter. It may give your server a longer life and free up CPU cycles for real business.