Need to extend disk(vmware). Need to determin what disk is what partition

So I need to extend a disk for one of our ubuntu machines.

The VM has 4 disks.

The problem is, I dont know which disk is what partition.

I have /med/mongoDB and /med/mongoDB-backup

Both of them are exactly the same size. 400GB.

I need to extend /med/mongoDB . How do I know, looking in Vcenter at the VM, what disk is tied to /med/mongoDB ?

Or do I have to do something stupid like, extend one of them randomly with a small amount and then see which is which? =)

Thanks in advance.

Regards

Greatness