External drive constant failure with iMac



I am experiencing constant setbacks when using my OWC external drive as a video/music storage.
My 2008, 24" iMac is in a perfect shape. The External Drive comprise of two, 2TB HDs connected in simple parallel inside the OWC box.

Connecting the two with FW-800, or USB-2 brings me the same results: after a few days of working (I can move videos and music files to the EHD) abrupt failure happens.
The External Drive loses all files, iMac can't see the drive, I am fixing EHD with the Disc Warrior or like, - all for the few more days of work, then it all happens again.

The HDs inside the External box been diagnozed as normal. Formatting them with the disc utility didn't improve performance.

I am dumbfounded, what can be this wrong with such a simple set-up?
Can anyone offer me advice?
My first thought is that the common item with the two hard drives is the case.
Maybe the interface electronics, or the power supply, in the enclosure.
OWC has very good tech support. Might be worth giving OWC a call with your concerns.

Thank you for the suggestion.
Indeed, I haven't call OWC with this thinking that simplicity of the setup is such that nothing could go wrong with it inside the EHD box.

I might use your advice though.
What messes up permissions and destroys all files is a bad dream of anyone who relies on back-ups or stores valuable files on EHDs.
My personal belief in them has been diminished badly.

Are both hard drives formatted Mac OS Extended?

Are the drives used independently (different data on both), or one drive with the other used as full backup?

Are the drives used with only one app, such as Final Cut Pro? or a variety of other AV software?

You said that a few good days pass before seeing the problem again.
Is there any particular circumstances that seem to trigger your EHD difficulties? - Something that you might not do every session, or every day? (That's just something to think about if the problem recurs.)