tracking per process IO usage / stats ... help needed..

[Joe Schmoe]

I have a FreeBSD system (4.9) running a fair number of
processes in a multi-user / shell hosting environment.

One problem that routinely comes up is that the system
will seem to be fine in terms of CPU, and none of the
top 10 or 15 processes that I see in "top" are using
much CPU ... but the load average is very high -
sometimes as high as 30 or 40 ...

I have good reason to suspect that the load is high
due to I/O.  I can see the number of processes
blocking on I/O in vmstat, and I can see iostat for
the entire machine, of course ...

BUT HOW do I see on a per process basis which
processes are using the most I/O time ?  It does not
help me to simply see that the system is using a lot
of I/O ... I need to know which processes specifically
are guilty, and to see them in some kind of ranked
order, just like "top" shows me for CPU usage.

So what would you recommend ?  Is there some way of
interpreting "top" to see that, or a way to tell "top"
to show me based on I/O instead of CPU ?

Any suggestions appreciated.

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