Is RAID1 volume usable while rebuilding RAID after disk failure? One disk of my 2-disk-RAID1-stack has failed and I'm about to replace it.

Is the volume usable—i.e. can I read &amp; write just as I normally could—while Disk Utility is rebuilding the RAID?
Yes, rebuilding happens in the background and the volume can be accessed normally. 

I/O performance might be affected, but in my own experience it's more likely the rebuilding process that takes the performance-hit—i.e. rebuilding would be faster if the volume wasn't in use.