Hanold is very correct. Raid 1 (mirroring) is only dulication write not read.
Also you are using a 3ware Switch that supports raid.
3ware, Escalade 7500-8, Eight Parallel ATA/133 Ports (1 drive/channel), 64-bit/33MHz Full PCI Card, Memory is embedded and 3ware has not responded to my requests for how much memory. I am guessing about 16k total based on a first generation card I have from 3ware.
The point I am trying to make is the DPT crew that started this company when they were aquired by Adaptec was not aiming for High end raid. I hope they release a High end card but the switch technology that they are using supports no inteligent thinking on the part of the card. No NTFS tables stored in memory, no buffering out-side the drive, no through-put caching, etc...
If you want to reduce mirroring load get somehing with an i960 chip and 128mb of ecc memory