Hardware RAID 5 Performance Configurations?

gandy909 asks: "I am facing the need to replace a major server in the next few months due to both EOL status and disk I/O bottleneck issues with the array containing the data. The server is configured with a 2 channel array controller. It is a RAID 5 array and has 4 drives, 2 per channel (2 data, 1 parity, and 1 hot spare). Obvious performance benefits in replacing the server are quadrupling CPU speed and doubling the memory. Other side benefits I will gain with the new drives, that I think should help my performance, are moving from u160 to u320, and going from 7200 RPM to either 10k or 15k RPM." How would you configure a larger array to best increase its performance? "Having googled around, the consensus is that increasing the number of drives is the preferred way to attack the I/O bottleneck. What I don't find much help on is determining the configuration of the larger array. Assuming I am going to be using a 12 drive array I have come up with the following possible configurations:

1 2 channel controller, 6 drives per channel
1 4 channel controller, 3 drives per channel
2 2 channel controllers, 3 drives per channel
3 2 channel controllers, 2 drives per channel

Would any one of those configurations provide better performance than the others, or would they all even out considering other factors?"

Comments

Well, knowing 0 about your business requirements.

[dnight]

I'd put 2GB fibre HBA's in the server(s) and attach an OpenSAN RAID box from Winchester Systems with dual-homed fibre to the array. That'll take care or your bottleneck and help your future scaling requirements.

Re:Depends on usage patterns

[innosent]

No, internal transfer rates are now up to around 109 MB/s for the top 15k RPM drives. You should be able to do better than 60MB/sec per drive, unless your reads are all over the place. (Lots of small reads instead of a few large, contiguous reads?) If you REALLY want speed, you can't beat RAID 10. For 12 drives, I would go with 2 U320 dual-channel controllers, having 3 drives on each channel (4 would probably be better, but that's 16 drives). Probably would be best to mirror across channels on the same card, and stripe those 6 (or 8) mirrored pairs across the two cards. You could hit a theoretical write speed of 640MB/sec pretty easily with 16 drives, probably only around 550-600 with 12, with read speeds of 1280MB/sec for 16 drives, and just over a GB/sec with 12. If a GB/sec isn't fast enough, it's probably time to write new software.