How does RAID0 work underneath, when the devices have different sizes?

To my surprise the CentOS 7 installer allowed me to create a RAID0 device consisting of roughly a 17 GB disk and a 26 GB disk. I would've expected that even if it allows that, that the logical size would be 2 * min(17 GB, 26 GB) ~= 34 GB. Yet I can really see a usable size of 44 GB on the filesystem level:

$ cat /sys/block/md127/md/dev*/size
16955392
26195968
$ df -h |grep md
/dev/md127   44G 1.9G 40G 5% /

How will the md subsystem behave performance wise, compared to a situation where the disks are equal? As it's impossible to do a straightforward balanced stripe across 2 disks.