Long I/O pauses on same mass storage

[A. Wright]

I have recently upgraded my system to 8.0, and in the
course of doing so, have migrated most filesystems
onto a new drive.

I have noticed, since the upgrade, several instances
where a very long pause occurs during which time one
or more process is in uninterruptible device wait.

This seems to most commonly happen when both reading
and writing tasks are active -- I am unsure whether 
reads writes must be in the same partition, or whether
two partitions on the same drive are sufficient.

These pauses are quite long, on the order of 10 seconds
or more, and happen during tasks that ran quite happily
before the upgrade (example: if doing a lengthy compile,
or subversion update, then opening an editor will "hang"
while attempting to open the executable).

As I am in the situation of switching from 7.2->8.0 and
at the same time using a new drive, I would like to
eliminate one of these from the equation first.  Before
I will be able to move on to chasing down the manufacturer
if the drive is faulty, I will need some good data.

While I will run some further tests here, I thought I would
ask:

 	Is anyone else seeing poor disk I/O scheduling or locking
 	behaviour in 8.0?

 	Is anyone aware of any of the filesytem changes that
 	have occurred since 7.2 that may explain this?

 	Does anyone have any thoughts on how to conclusively
 	prove that the drive is at fault?  I have not seen any
 	errors logged to dmesg.

Thanks,
Andrew.