Okay, so I have:

2x2.8 GHz Quad-Core Intel Xeon (8-core) Mac Pro
with 18GB of 800MHz RAM
and the NVIDIA GeForce 8800 GT w/512mb VRAM
Running Snow Leopard

All of my footage is stored on a Drobo, which I've had no issues editing from in the past.

However, when I attempt to open a 1080p ProRes 422 HQ movie file (which was transcoded from a H.264 file from my Canon T2i) It plays for about 2 seconds and then the frame freezes while the audio continues on. It doesn't matter if I open the clip up in QuickTime Player or if I'm working with the clips in Final Cut Pro, it seems to play the same amount of time and then the frame freezes.

Does anyone have any recommendations for improving playback and editing performance? I'm expecting to be able to apply color corrections and other filters and still be able to preview edits without rendering.

Thanks in advance!

OK, since no replies yet I'll start them off.

Try the "normal" ProRes (not the HQ one.... I'm still on FCS2 so forget what Apple calls them all now). I think it may be termed LT.

Also, how is this Drobo connected? FW800 is way, way better than USB (if that's an option).

How were these files transcoded? It does sound like a problem with the Drobo's connection to the computer. Transfer one file to the Mac itself and see if you have the same problem.

OK, since no replies yet I'll start them off.

Try the "normal" ProRes (not the HQ one.... I'm still on FCS2 so forget what Apple calls them all now). I think it may be termed LT.

Also, how is this Drobo connected? FW800 is way, way better than USB (if that's an option).

I'll try non-HQ ProRes, is there any significant quality difference?

The Drobo is connected via FW800.

How were these files transcoded? It does sound like a problem with the Drobo's connection to the computer. Transfer one file to the Mac itself and see if you have the same problem.

They were transcoded with Compressor, I'll test out the files on a SATA drive and see how that goes.