Hi, both of my /dev/hda and my /dev/hdb contain /boot partition. I'm wondering how to tell which harddrive's /boot is actually being read? Thanks

Shutdown the server. Remove the power from one of the drives. Power back on.

Of course, there are other ways

Very good question. In theory your BIOS should have a predictable search order or a configured device to boot from.

Alternativly do

"mount"

and see which partition is mounted as "/"

Check the boot partition config files on both drives and check to see which volume is supposed mounted as root and see if it matches the device you got from the above test.

If different then your question has been answered.

If the same then use fdisk and check to see which partitions are marked as bootable.

Confirm you can boot from a Linux standalone CD and mount both boot partitions.

Change the config files in each partition to different bogus partitions and reboot, see which partition linux cannot find when you reboot. Then whichever boot partition you told to use that bogus partition is the one it was trying to use.

Use fdisk to enable/disable the boot flag on the boot partitions to confirm.