Need to find out which process is hitting hda

I'm using centos 5 as the OS so, there's no fancy dtrace to look at
which processes is causing my disks to thrash.

I have 4 disks in the box. (all ide, 7200rpm)

1 OS disk [hda]
2 raided (1) disks [hdb/hdc]
1 pg_xlog disk (and also used as an alternate tablespace for [hdd]
temp/in-transit files via select, insert into tmp table. delete from tmp
table, insert into footable select * from tmp table)

Problem now I see from both atop and iostat, the Device: (iostat -dx 10)

rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
hda 98.60 14.69 121.98 15.08 1775.02 2908.29 34.17 47.53 551.67 7.29 99.95
hdb 0.70 4.20 16.48 2.30 304.50 51.95 18.98 0.21 10.94 8.45 15.86
hdc 0.00 3.40 12.49 2.00 223.78 43.16 18.43 0.07 5.04 4.42 6.40
hdd 0.00 56.94 0.50 3.70 53.55 485.91 128.57 0.02 5.48 3.95 1.66
md0 0.00 0.00 29.57 11.89 526.67 95.10 15.00 0.00 0.00 0.00 0.00

the number of writes and reads on hda is much greater than expected and I'm not sure who/what is causing it.

Thanks for any clues.