RAID 6 Performance using MD

So I'm thinking about creating a NAS for my house with somewhere between 12-24 disks in a RAID 6 with software RAID, RAID 5 is not an option. I've looked a bit trying to see the performance of using RAID 6 on so many disks but couldn't find anything. I've heard that anything higher than like 6-8 drives MD RAID 6 doesn't scale very well but that was awhile ago. Is this still true? Where can I find some more information on this? I figured of all people you guys would have encountered something like this before and might be able to point me in the right direction. Thanks!