This may be somewhat of a silly question but here goes. Today I replaced a 2TB drive in my array with a 3TB drive, the array is currently rebuilding. What happens if I copy data to the array whilst its rebuilding? Is it a bad thing or do I not need to worry about it?

The rebuild will still continue but will slow down during the copy process.  No harm done.  But I do try and avoid it if only because of the thrashing that happens to the drives in question

Agree ... while it will work correctly, it's not a good idea to use the array during a rebuild.

 

Remember Murphy's Law!

 

 

I try not to temp the fates when rebuilding.