zfs question

I have a simple question about zfs.  I have a 4x4T zfs raidz1 array that 
has worked perfectly for years.  Recently, a disk in the array went bad, 
so I replaced it with a spare 8T drive that I had on hand.  My 
understanding is that that the array would only use 4T of that drive, 
and moreover, that would be true even if I had to replace two more 
drives with 8T disks.  However, if I replaced the last drive with an 8T 
disk, so all the disks were now 8T, would the array use all the of the 
8T on each of the drives, or still be a 4x4T array?

-- 
Rick