How do I... Recover my recorded(?) audio

I’d like to ask for advice and share my experience.
Two days ago I recorded DJ sets at a local festival. After last year, when all audio was unusable probably because of buffer-underruns, I wanted to do it right this year.

The setup I used is: MacBook Pro model 4,1 (newest of the previous generation), Edirol FA-66 interface, recent JackOSX and Ardour 2.8 revision 4919. I had a stereo analog feed from the mixer and a microphone pointed at the audience on their own separate tracks. At home, I recorded my mp3 player for hours without interval and all went well, although this test setup was only one stereo track.

During recording I made sure to monitor through Ardour (one of the mistakes I made last year was monitoring the hardware “direct input”). All was okay, I soloed either track once in a while to check for audio, I looked at the meters in Ardour to prevent clipping and it all seemed fine.
One thing I didn’t recognize as “wrong” (that may be my Big Mistake this year) is that after (I think several hours) of recording, Ardour stopped updating the track waveforms for both tracks. I could still hear the audio through the (still Ardour) monitors, so I assumed it was just the graphical part - I had seen this before in other software.
After a few hours of recording, one artist who “needed space” had closed my laptop, but when I opened it again, it continued - I thought it would have gone to sleep, but apparently it hadn’t. Phfeww!
Later that evening one DJ told me that the laptop showed an error. This was true: the disk was too slow to write to. My laptop does have a 5400 rpm disk, but looking at the Activity Monitor of OS X, the write peaks were at 6 MB/s which seems not too much. Does anyone have experience with this? I myself think (and hope) it might have something to do with the fall protection mechanism that blocks write access when moving heavily, which the DJ booth allowed for when the people on stage danced. When I came back, found that the recording had stopped, I started the recording again and in the new region, waveforms were plotted. In the first region of the “audience” track, waveforms appeared after closing the dialog for the “disk too slow” error. The “dj” track didn’t show waveforms.

Afterwards I checked and found several 4 GB files that should contain the audio for the first 6 hours of recording. But when I opened one for previewing in iTunes, it only played the first 11:49… Opening the project in Ardour gave “File missing”, but I didn’t do anything to the files. The region that should have had audio in it for 6:24:30, only shows waveforms for 11:49 and silence for the rest. I’m absolutely positive that I heard the audio that went into the track, and that the track was armed for recording, and that it wasn’t muted during recording.

Now I’m fearing that I’m stuck with two times about 4 GB of silence. Is there any way of telling that this is really silence? How do I know what happened?

I’ll happily try to give more details, but now I’m still frustrated… Thanks in advance for reading and any replies.