[CentOS] which process & file taking up disk IO?

I'm having load problems on a server. The bottleneck appears to be disk IO.

iostat would show ~100, under %util, during peak usage.

i'm running things like clam antivirus, pop, exim, apache, mysql on the server.

is there a way to check which process and which file is taking up disk IO? or
see what is being written to the disk?

i'm very puzzled as the amount of writes is 10 times higher than the reads; and
I can't figure out what the writes are for.

Device:    rrqm/s wrqm/s   r/s   w/s  rsec/s  wsec/s    rkB/s    wkB/s avgrq-sz
sda3         2.20  32.94  2.12 17.42   34.54  407.74    17.27   203.87    22.63

avgqu-sz   await  svctm  %util
   1.28   65.38   5.10   9.97

Is it normal for the %util to be 9.97% for the above reads/ writes on a U320
drive? or perhaps i have a badly misconfigured server? the drive is 2 x 146GB,
RAID 1 using the LSI logic LSI22320-R card.

#elvtune /dev/sda

/dev/sda elevator ID            1
        read_latency:           2048
        write_latency:          8192
        max_bomb_segments:      6

#cat /proc/sys/vm/bdflush
80      50      0       0       600     10000   80      70      0

Server is running CentOS 3.5; CPU and RAM are very much under utilised.

Regards,
Wee Cheong