Sudden data failure on Huge U320 drive

1. This was an odd one. I was working on what I was thinking was
perfectly healthy drive whilst using FCP, and suddenly FCP
Grab and Capture says "can not find movie"

2. I apple-tab to finder and whilst navigating the directory
structure I click on a folder that said about 50G .

3. As soon as I click on this folder its filesize changed to
50M or so.

4. I realize this isn't right so I shut down the Mac to do a
restart.

5. The Mac (an Apple G5 Dually 2.5Ghz with 2G Ram connected to two 1.2TB Huge Drives) boots up and can not find Huge #2
(the drive with the magically folder size change)
(these are totally independent drives powered by a dual
channel SCSI UL4D).

6. I run repair permissions and reboot.

7. OS X can not find Huge #2.

8. repeat step 7 a few more times.

9. Run Disc Warrior which finds Huge #2 albiet it is not
showing on desktop.

10. Run Disc Warriors "rebuild" functions.

11. Most projects on drive either disappear (o byte folders)
or are sent to the "rescued" directory where they become
usually unplayable movies.

12. Anyhow three days later the drive is "fine" in a sense it
works but has totally dumped important projects that were ready for mastering and backup that day; but they never made
it due to the magically disappearing folder.

13. This has stumped our vendor, and me.

Has anyone any suggestions?

p.s. I'd be glad to add any further information if
needed....

Thanks is advance

Mark Pigott