I was told this last week by a buddy that builds Macs. Quized him this morning and here is what I got back:
I couldn't find all the articles I read last week, but in the following, I did read it wrong. This is referring to a FW800 add in PCI X card for running a multiple drive array.
Have to do some more checking to see if it's the same on the Mac's internal FW 800. http://www.barefeats.com/hard35.html
Last November we discovered a problem with multi-channel FireWire 800 RAID on the G5. The sustained WRITE speed was much lower than SATA... AND... much lower than a Dual G4/1.42 Power Mac with the same configuration (see second graph above).
I've asked around as to why the G5 could only achieve sustained WRITE speeds half that of the G4. Nobody has any hard answers. Only theories. Some blame Apple's PCI-X controllers. Some think it's a G5 firmware bug. Some think it's a deficiency in the PCI controllers or an incompatibility between those controllers and the G5's PCI-X slots.
Two of my colleagues in two other labs with similar setups observed the same phenomenon. We tried different drives, different case kits, and different PCI controllers -- same result. We even tried putting one FW800 card in slot 4 (133Mhz) and one card in slot 3 or 2 (100MHz - different bus) -- same result.
I'm hoping Apple engineers can help solve this mystery since I've passed my findings on to them. I hope it's a simple firmware fix or OS patch -- and doesn't require a Rev B motherboard!
Just offered for your info - don't want to start a range war over this.