Host Adapter Performance Shootout
After I finished my article comparing SCSI and IDE technologies ("SCSI and IDE: Defining the Differences," June 1997), several readers wrote asking me to review SCSI host adapter performance. Representatives from several SCSI host adapter vendors also asked for such a review. I've wanted to do this type of head-to-head comparison to test how the performance and efficiency of the current crop of SCSI cards stack up.
So, I set off to obtain a cross section of SCSI host adapters representing some of the most popular and outstanding cards for Windows NT systems. I'll show you the results of my SCSI performance shootout and provide a few tips to enhance your SCSI host adapter's performance under NT, regardless of which product you own. This article focuses on regular SCSI host adapters rather than hardware RAID or caching controllers that incorporate SCSI. Therefore, this article is most appropriate for workstations and low to midrange servers rather than enterprise-level servers.
Rounding 'Em Up
I reviewed products from five SCSI host adapter vendors. The vendors are Adaptec, Advanced System Products (AdvanSys), Mylex/BusLogic, QLogic, and Symbios Logic. These manufacturers supply most SCSI host adapters in use on NT systems around the world. They also supply most embedded SCSI controller chips on system motherboards and RAID controllers.
Each vendor provided an Ultra SCSI-capable host adapter. Some vendors could provide only single-channel or narrow SCSI adapters, so I decided to use a narrow Ultra SCSI hard disk (a Seagate Medalist Pro ST-52160N 2GB 5400RPM Ultra SCSI disk and two Cheetah 4LP ST-34501N disks) to represent a least common denominator for the adapters in this review. All the SCSI host adapters I reviewed use single-ended termination. For specific information about each host adapter, see the sidebar, "The Contenders," page 187.
For my test system, I configured a 200MHz Pentium-based system with 48MB of RAM and 512KB L2 cache, running NT Workstation 4.0 with Service Pack (SP) 3. My benchmarking software was U Software's Bench32 version 1.21. Bench32 is an excellent system benchmarking utility that provides comprehensive yet intuitive configuration options for disk, CPU, memory, and video performance benchmarking. For the tests in the benchmark suites, I used a 4KB block size and a 1MB test file size (Screen 1 shows Bench32's disk test configuration screen). In addition, I disabled all nonessential services on the test system and rebooted the system before each test to ensure a common system memory load. I attached the test hard disks used for performance benchmarking as the only devices on one channel of each Ultra SCSI host adapter, with no other SCSI devices present except the adapter. I used this configuration to ensure optimal SCSI bus performance and to eliminate the possibility of SCSI bus contention interfering with the tests. In another effort to eliminate possible contention with the test drives, I used a separate SCSI channel and controller for the drive containing the system/boot partition.
Are Newer Drivers Faster?
In addition to testing the performance of various Ultra SCSI host adapters, I wanted to test the potential benefits of using the latest drivers for these cards. NT 4.0 ships with drivers for most SCSI host adapters, and I wanted to find out whether you can improve performance by using newer versions of the same drivers obtained from the manufacturers. For each card I reviewed, I tested the native, shipping version of the SCSI host adapter driver (if available) and the latest version of the driver from the vendor's Web or FTP site.
Table 1, page 188, lists the SCSI vendors for the cards that participated in this review and the URLs for obtaining the latest drivers, and, where applicable, Flash BIOS updates for their products. The results tables later in this article provide head-to-head comparisons of original versus latest driver performance. By the way, to update a SCSI adapter's driver, you have to access the SCSI Adapters control panel in NT, as you see in
Screen 2.
Test 1:
Single-Drive Test
For the first performance comparison, I executed a straightforward test. I placed an Ultra SCSI hard disk (a Seagate Medalist 5400RPM Ultra SCSI 2GB drive) by itself on one channel of each SCSI adapter and ran a disk test suite on an NTFS-formatted 2GB disk partition. I designed this test to show what, if any, performance differences exist when you use different Ultra SCSI host adapters with a one-disk configuration. I hoped to find out which host adapters best maximized the test disk's performance potential. Although all host adapters adhere to the same specifications in theory (Ultra SCSI compliance, 20MBps signaling rate) and should therefore deliver approximately the same results, I had a feeling that this test would show some performance differences among the various adapters. Table 2, page 190, shows the results of this disk test.
The test measures drive throughput in MBps and applies an overall disk score in terms of average MBps and a Bench32 DiskMark score. As you can see from the table, the scores were far from identical. Although my test disk topped out at a maximum score of about 169 DiskMarks and a 3.76MBps average transfer rate, some SCSI host adapters were unable to exploit this potential.
In particular, I was surprised to see that connecting the test disk to the Adaptec AHA-2940U adapter caused the disk to achieve roughly two-thirds the total performance it was capable of when connected to other adapters. This result was especially surprising given Adaptec's popularity in the SCSI adapter market. The stark difference in results prompted me to re-run the test several times to ensure that I hadn't obtained any anomalous results. Successive tests (even with different cards and firmware revisions of the card) yielded very similar results. Adaptec has a strong reputation for compatibility and reliability; however, the company apparently lags behind other vendors in terms of SCSI host adapter performance. The fact that the Adaptec AHA-2940U continues to fetch a high price compared with its competitors also means that this adapter has a fairly low price/performance ratio (something to keep in mind if you're looking to buy the most bang for your SCSI buck).
In regard to the differences in driver performance, I also discovered some interesting results during the first test. Although most cards exhibited only minor or insignificant performance increases when I installed the newer drivers, one SCSI host adapter, the Mylex/BusLogic FlashPoint LT, gained significant performance when I used the latest driver (from 150 DiskMark points to 169 DiskMark points, an increase of almost 9 percent). As you can see from Table 2, page 190, none of the adapters I reviewed showed a decrease in performance going from the original drivers to the newer drivers.