Here is a tip from an owner of 152 partitions
from 2 Pata and 2 Sata.
Duck2006 advice is the one to go for first as you will known the complete list of all partitions of every disk in the box tabultaed in Linux convention.
Next you want to know the disk order the Bios has arranged as Grub uses the order handed down by the Bios. Grud can call sda5 either (hd0,4), (hd1,4) or (hd2,4) depending it is the 1st, 2nd or the 3rd disk. Don't blame Grub as you are supposed know how your own disks are arranged in the booting queue, right?
Linux doesn't use the Grub convention so you have to aks Grub to report to you. You can do so by invoking a Grub shell and then instruct Grub to tell you the geometry of each disk by commands (1st command is to invoke a Grub shell)
unitl all the disks have been viewed.
From the disks geometry, which also tabultes the partition ID and sizes, you then know which disk has the sda5.
Hope this help.