disk perormance

hi everybody,

when i switched to osx i did the 148 firmware update for my medea raid rtr 5..
i've been using the raid in os 9, and the raid works fine for playback in osx..
the only problems that emerged are when exporting or rendering all of a sudden
the system "looses pace" somewhere during the render/export destroying some frames,
and works fine thereafter rendering the rest of the file correctly
this problem doesn't occur when exporting to the internal HD (so it seems to be a read/wwrite problem with the raid)

checking the disc performance i get an read average of 51MB/s and write speed of 90MB/s.
the disk is pretty full and i'm about to erase the disk now.

my next step will be updating to firmware 149.
i think that i have to initialize the disk itself, probably using Atto express pro tools 2.8.2..
(we haven't express stripe..), although i'm a little concerned for i have heard of problems that my reseller had concerning a throughput of 1,5MB/s!!

any ideas which transfer rates should be appropriate???

my system
G4 dual 1ghz
1,5 gb ram
radeon 9000
UL3d

thanx for your help

stefan