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Power Computing provided the information in this article and it was deemed accurate as of 14 November 1997. Apple Computer, Inc. is not responsible for its content. This article is being provided as is and will not be updated in the future.
DISCUSSION Performance tips: 1. Use Fast/Wide or Ultra/Wide PCI SCSI-2 controllers and drives. 2. Use a dedicated boot drive. Some of the settings for Stripe performance may not be of benefit for the boot drive. By using a disk that is not involved in the Stripe will ensure that OS System reads will not interfere with overall Stripe performance. 3. Add a 3rd disk to the Stripe. More than 3 disks on a single controller will give you no substantial benefit because of SCSI overhead. 4. Use 4 disks and 2 controllers. For Mirrors, the benefit of using a second controller is a 5 to 25% speed boost. For Stripes, a second controller isn't too handy for a 2 disk configuration, but with a 3 or 4 disk Stripe and 2 controllers will give you the best results. 5. Get the fastest SCSI drives available. 6. Use 2 identical drives in the array so that the performance difference between drives is minimized. 7. Get the highest rotational speed available. (7200 minimum) 8. Buy drives based on sustained throughput not burst. 9. Drives with a higher amount of cache (512k or 1M) are better. 10. Software settings: For fine tuning, do not rely on benchmarks, but do your comparisons with your own software. Make the changes one at a time. SCSI Disconnect: Turn it on. Write Cache: Turning Write cache on can improve write performance significantly. Sometimes it is turned off for Mirrors for greater safety. Stripe Segment: 100 blocks (51,200 bytes) is optimal for most environments. If the drives have a sufficiently large cache and the application uses large I/O chunks, try experimenting by turning this up. Test changing cache and buffer configurations: Some drives will permit SoftRAID to change the cache segments. Sometimes, setting this lower will improve performance if the Stripe unit size is increased. You can also change the cache flush size. If you are uncertain of the impact of these settings, it is recommended you not change them, since the wrong settings can have adverse affects on system performance and reliability. Format the disks occasionally. As bad sectors are found, performance degrades any time the computer has to read past that sector, even if it's mapped out. Reformatting the drive renumbers the blocks to keep them consecutive. This should only be a factor on old drives, but reformatting twice a year is not a bad idea. Use only the outer areas of the disk in a Stripe. Some users claim to get a 50% speed boost using this. To do this, reformat the drive and create the Stripe using the first partition on each drive and the partition size less than 50% of the drive. 11. Place arrays on their own buses. Avoid putting CDs and Scanners on the same bus as the array. Higher numbers have higher priority on the SCSI chain so make the RAID drives as high a number as possible, if you must share your RAID bus with the rest of your SCSI. 12. Minimize Extensions which affect performance. Some Extensions can have adverse affects on the performance of the system. Generally, keep the Extensions as minimal as possible. There are shareware utilities to check performance in relative terms. One, called Check Ticks, makes 10,000 calls to the system and counts how often it's interrupted. More than 1000 is an indication of slower than optimal performance, but this only measures one type of system performance. Lots of other third party utilities will measure other factors. 13. Cabling. Cabling is critical for performance. Low quality cables can cause system instability and data corruption. See PowerSource 1515 for information on optimal SCSI setup. 14. Use current Technology wherever possible. UltraSCSI is currently available and SCSI-3 Fiber Channel is on the way. Machines Affected: PowerTower Pro with RAID |
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| Document Information | |
| Product Area: | Computers |
| Category: | Power Computing Corp. |
| Sub Category: | Troubleshooting |
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