Can you use the hard drive while mirror set is rebuilding?

I am using RAID 1 (Mirrored) configurations. The status is degraded, and Drive A is online, but Drive B is Rebuilding. Can I use Drive A while Drive B is rebuilding? Or is it best to leave it alone?

I have found that you can continue using Drive A during the rebuilt. What drives are you using? WD recently told me that their My Book drives are NOT suitable for use in a RAID, so be cautious.

I am using My Book Thunderbolt Duo, so I am using the drives that came in the enclosures.