[Bug-ddrescue] Question about identifying which disk has data on it

[Will]

Hello

Thank you for this software and apologies if this is not the correct place to 
ask this question.

I have a disk that I need to clone using ddrescue. It is a disk that is part of 
a raid from a server. I have a disk to clone to which is identical to the 
source disk.

I type 'fdisk -l' to list the disks and I can see /dev/sda and /dev/sdb

As my disks are identical I cannot identify which is the source disk and which 
is the disk to write to using the information from fdisk -l

Q1 - Is there a command I can use to find out which disk is which? One has data 
on from the raid, the other is brand new and has never been used.

Q2 - I then intend to use
root# ddrescue -r-1 -n -S -v /dev/sda /dev/sdb recovery.log
to clone from sda to sdb
Is this correct please?

Thank you very much for your time and I apologise for this being such basic 
question!