Disk/FS I/O issues in -CURRENT

Hi folks,

I am having some very weird problems on my laptop, which I at first
thought were due to a failing drive. However after a lot of testing and
trial and error I've concluded that it must be a software problem - I'm
smelling filesystem issues or something.

Whenever I transfer large files to or from my harddrive, I will *always*
get a lockup after ~480 MB transferred. Example scenario:
- I use another machine to FTP to my laptop.
- I start downloading a file of about 700 MB, and after ~480 MB it
simply stops. The HD led on my laptop goes off, I can switch VTs but
nothing else. Even keyboard input is non-functional.
- After a few seconds another small burst of data (perhaps a few hundred
KB or something) will go through, keyboard buffers will be processed,
and then it freezes again with only one option - power off. C-A-D is a
no-go. The IP stack is up though, I can ping the machine, and I can
still change VTs.
- If I pause/cancel the download immediately when it freezes, my laptop
will come back to life a few seconds later. I can then start downloading
another file, or resume the file I had started - everything seems to be
back to normal. But whenever I hit ~480 MB transferred from *one* file,
it will freeze again.
- Downloading many smaller files in one batch, that sum up to >500 MB,
is not a problem.

All the above points applies to data transfer in the opposite direction
aswell. 
Another way to reproduce this is doing a 'dd if=/dev/random of=testfile
bs=8192', or the other way round - eventually (and after between 450 and
500 MB - a bit hard to tell) it will freeze.
However, if I use a partition as the output instead of a file, it will
*NOT* encounter any such problems.
Transferring files between two partitions on the same HD also seems to
work fine - atleast when using Midnight Commander.

I first encountered the problem when using unison to sync my /home with
another machine, and it got a hickup when it started finding these large
files (ISOs and the like) and was scanning them to produce a checksum.
Once I moved the large (>450 MB) files out of the way, it worked nicely.
When I started copying the files over manually, I experienced the
freezes again. Moving the files to another partition before copying it
to the external machine did not help the issue.

I have ran the Drive Fitness Test from IBM (this is a ThinkPad T21)
twice, and it finds no errors whatsoever. And I know for a fact that
this problem did *not* occur with 5.1-RELEASE, as it was with that
version I copied the files to my disk in the first place.

I hope this information makes sense to someone. I suppose this is the
punishment for following -CURRENT - but unfortunately 5.1-RELEASE had
other issues that I couldn't live with.


Best regards,
/Eirik