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PCI SCSI Card vs. Onboard SCSI:
Tests with Narrow Ultra-SCSI Hard Disks
Published: 10/21/98
The following is to compliment Mike's excellent article about stock Ultra-Scsi Hard disks coupled to a PCI SCSI card . In that article, the results showed lilttle or no benefit of using a PCI SCSI card with the IBM 9600 stock narrow drive. As Mike indicated " You won't 'see' a real improvement in speeds on these drives in most cases, as the onboard SCSI of most Macs is 10MB/sec, faster than most narrow SCSI drives can sustain. "

Mike also mentionned that he wasn't sure if the lower scores he was seing with the PCI SCSI card coupled to the stock IBM drive was caused by the use of the 9600 kansas motherboard during the tests. In case you missed that tidbit, the PCI video card scores in the 9600 are usually up to to 25% slower than they should be based on tests in comparable speed Mac models not based on the Kansas motherboard. [See the Mach 5 systems page-Mike]

Recently , I took advantage of the lower pricing on PCI Ultra-SCSI controllers, (especially the Jackhammer which was recently seen as low as 139$! ). While waiting for a new Seagate Cheetah UWide disk, I decided to verify the performance of some of my narrow drives coupled to the JackHammer since Mike's results may vary with other disk drivers or narrow disk models.

To satisfy my curiosity I tested the Quantum Fireball 2GB (stock 7600), the Seagate Medalist 2GB and the IBM OEM DHFS 4 GB hard disks in my 7600/330 (powerforce 220/110 overclocked to 330MHz) with the Jackhammer Wide SCSI PCI card. I compared the results obtained with the 7600's 10MB/sec onboard SCSI to see what benefit if any would be obtained. As predicted, sustained rates were not much better with the PCI SCSI card as the drives were capable of only 5 to 7MB/sec sustained rates (to the exception of the IBM DHFS who did a nice 7-8 MB per sec in some tests) according to the ATTO benchmark tests. There were cases where peak rates were much higher with the PCI SCSI card, especially with the faster narrow (IBM DHFS) but my feeling is that these monster scores (sometimes 80 mb/sec) do not reflect the reality as the drives specification are by far exceeded . I will show here the results obtained for sustained write or read tests using the ATTO benchmarking utility. The ATTO Benchmark tests were run at all possible settings, representing file transfer sizes of up to 32K, 128K, 512K, 2MB and 8MB. The smaller file sizes would be indicitive of database applications for instance, the larger ones applications like video capture. As you will see. the PCI SCSI card scores were actually slightly slower in some limited cases but many times the results showed a 10-15% improvement over the Onboard SCSI.

Test System:

  • 7600/330 (powerforce 220/110 overclocked to 330MHz)
  • OS 8.5
  • 224MB RAM (VM Off)
  • 7MB Disk Cache Setting (not used in Benchmark tests)
  • Stock 4GB IBM Hard disk - model DHFS 34330 (2 GB Free)
  • Seagate Medalist Hard disk 2 gb
  • Stock Quantum Fireball 2 GB 7600 HD.
  • Power 3D voodoo card in PCI slot 2 (middle)
  • JackHammer Wide PCI SCSI card SE in slot 1 ( near the CPU))
  • Speed Doubler 8.1.1 (8.5 compatible was used in some tests)
  • All drives showed light fragmentation and were full at 50%.

Summary of Results:

Benchmarks:

Sustained READ

Generally the use of the Jackhammer PCI card showed no improvement over onboard SCSI with all 3 narrow drives tested with the exception of the Seagate Medalist and the Quantum Fireball whose scores were dramatically higher in 32k files size test (nearly 200%). The biggest surprise was seen with the Fireball. In this case , the use of the PCI SCSI Jackhammer card decreased the performance by a shocking 50% with larger files !!!

To have a better idea of everyday performance, I performed other tests in which I used Connectix Speed Doubler 8.1.1 as well as the system cache to see what kind of improvement I would get. As expected, Speed Doubler and the system cache boosted the performance in all tests , sometimes by as much as 12 times (32 k file test) compare to using the Jackhammer alone.

Sustained Write

Also in these tests , the use of the Jackhammer showed little or no improvement increase over the onboard SCSI. Again, the scores obtained with the Jackhammer coupled with the Quantum Fireball were exceptionally lower, decreasing by as much as 30% in some cases. For the other two drives, the scores were identical.


Drivers performance tests

Conley vs Apple

In a final series of tests, I wanted to see if Conley's drivers (2.02) would provide any additionnal benefit over Apple's newest drivers (supplied with MacOS 8.5). The scores obtained with the IBM and Seagate drives showed a general improvement of disk performance in all tests when using Conley's drivers. The benefit was generally close to +1 Mb per second, or about 15% up over Apple drivers for files over 512k. With the Conley-IBM drive combo, the performance was decreased in smaller files tests by about 20%, suggesting that Apple drivers are better suited for drives like the IBM DHFS if it is going to be used for general purpose and not for audio-video applications. Since the results were opposite with the Seagate Medalist, I think there is no rule-of-thumb that can be applied. It is better to verify yourself which driver is better suited for your intended usage.



Conclusion

Coupling narrow drives to a Wide SCSI PCI card like the Jackhammer will show limited improvements with fast narrow Ultra-SCSI drives over the onboard SCSI bus. If you intend to use the SCSI card with slower (5400 RPM) narrow drives like the Quantum Fireball (stock 7600), the performance will most surely be decreased.This might come from the use of a smaller disk cache in the Fireball (128k vs 512k for the Medalist and the IBM OEM).

If you intend to get a fast wide Ultra-SCSI drive in a near future, then a PCI SCSI card is a solid investment (see other articles in this section) . If not, the improvement provided with narrow Ultra-SCSI drives does not justify the price.

Frank Bernier




Other site SCSI reviews:
For more SCSI tests with all the popular PCI SCSI controllers and wide drivces, see the site's SCSI Features page. For general information on SCSI basics - check out the SCSI area of the Links page.


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