Do I need faster RAID speed?

Question

I have a clip that contains 4 layers of 4K R3D files (2 layers of masks + 1 layer of rotoscope + original layer) that are dynamically linked to After  Effects.  The  footage was shot in Redcode 36.
When I turn off GPU acceleration (so, software only), the bar goes red in  the timeline.  I activate GPU acceleration, the bar goes yellow in the  timeline.  Now, correct me if I'm wrong, but that yellow line means the  clip is now GPU accelerated and it may be possible to play it back in real  time (at some resolution...maybe 1/16?).
I play the clip.  The audio plays fine, the video doesn't play at  all, no matter what the playback resolution is set at.  It just stops  cold on the first frame.
I check Activity Monitor.  The CPU is hitting around 40% (sometimes less, sometimes more).  The RAM has a few GB free.
I'm on a 5.1 (2010) quad Mac Pro (3.2 GHz) with 32 GB RAM, and PP 5.0.3 on OSX 10.6.5.
QUESTIONS:
1  a) Is it possible that the bottle neck is the hard drive read and write speed? 
I have an external Raid drive (4 x 2TB) connected with eSata.  I tested  it with AJA System Test.  The read and write speed are 125MB (read) and 105MB (write).  Right  now, it's limited by the eSata card I have which caps everything around  125MB.  If I get something like this:  http://eshop.macsales.com/item/Newer...gy/MXPCIE6GS2/
I can get sustained rates of 220 MB (read) and 180 (write) from my external RAID drive (according to LaCie's website). 
b)  If I'm editing 4 layers of 4K files at 36 MB each, in theory, I need  sustained read and write speeds of 144MB (4 x 36MB) minimum, correct?   Am I way off base here? 
2.  Another thing that's confusing me is how the playback resolution  factors into all this.  If I set it to 1/16, what sustained read and  write speeds do I need to play back the clip (all 4 layers) in real  time? 1/16 x 144 MB = 9 MB.  Do I only need 9MB of sustained read and  write speeds to play back the clip in real time?  Is that how it works?   If so, how come I can't get it to play back in real time?
3)  Is there a software (for OSX 10.6.5) that can measure whether or not  the hard drive read and write speeds are peaking?  Apps like AJA System  Test don't measure the hard drive when in use.  I'd like to determine  if the hard drive read and write speeds are being strained/ pushed to  the max.
Any help would be appreciated.  Thanks!

Answer 1

I have a similar setup and use BM for I/O.
They have a great piece of software for testing drive i/os.
Tomorrow I may get on my system and get the exact figures of drive I/o that are required for what you need.
My internal array runs at around 210mbs bothways and I still get the
issue you described. So I guess if your thinking of uping your array to a similar speed
your issue may not be resolved. I did think that the yellow indicator meant it could play in RT.
I found on a Vid Tut. from Adobe TV (I couldn't find the link) I think it was "optimising your system"
It showed a yellow indicator on a timelione that could not play. They said this was due to the drives
not coping. Looking forward to a faster array when they are cheaper, I think around 300mbs should
do the job.