I have no idea why I got this error, but I did. I guess it comes up when
it tries to access BLK 200512 since fsck caused to to happen a bunch of
times.

Here's the error:
sd0(esp0:0:0): medium error, info = 239774 (decimal), \
data = 02 f2 03 45 aa 00 00 00 00 00
CANNOT READ: BLK 200512

It seems to have gone away after I ran fsck over it a few times...I'm
sitting here with my fingers crossed.
My computer is a Quadra 650, the kernel is my own (GHOST-PRIEST #1), which
I've been using ever since I compilied it (Oct 22). It's a 1.3_ALPHA
kernel, I got the same error using a more recent kernel (from a few weeks
ago). I'll be happy if this doesn't come back, but I'm afraid it might be
a sign of a failing hard drive...
-Xiamin