OT - drives in a RAID5 configuration

[Jonathan Horne]

i would like to ask my freebsd peers a hardware question:

my  FreeBSD 6.0 server has a 3ware 6800 8 channel IDE raid controller.  
configuration is 6 disks, 4 120GB disks (/opt) in RAID5, and 2 76GB disks in 
RAID1 (everything else).  one of the 76GB drives has failed.  i have a few 
options that i could persue, but one option i need some advice on.

i have another 120GB disk here at my apt, but its not the same model as the 
other 4 120s that are currently in the server.  they are otherwise identical, 
but the 4 have 8mb cache, and the one here has 2mb cache.  if i eliminate the 
76GB RAID1, and (break/rebuild) the RAID5 with the additional 2mb chace 120GB 
drive, what kind, if any, performance degrdation would i expect?  in a 
hardware RAID5 configuration, does the cache on the drive play a major role?

on a related note, is anyone using any 3ware controllers in FreeBSD, and is 
there a way to monitor status (healthly, failed) from within the OS?

thanks all,
jonathan