varied drive size raid10

Hello,

When using raid10 btrfs on four disks of two different sizes (two of one size two of another) does btrfs know to match the similarly sized disks in a mirrored pair?

I guess a corallary would be: will btrfs stripe over the mirrored pairs until the smaller pair fills up and then continue writing to the larger pair?

Also, if raid10 is used with, say, 3 100gb drives and 1 250gb drive would the 250gb drive be able to fail without data loss? Could it be fully utilized? How about with a 500gb drive?

Thanks,
Brian