[CentOS] OT: What's wrong with RAID5

Hi all,
Sorry for the OT.
I've got an IBM N3300-A10 NAS. It runs Data Ontap 7.2.5.1.
The problem is, from the docs it says that it only supports either
RAID-DP or RAID4.
What I want to achieve is Max Storage Capacity, so I change it from
RAID-DP to RAID4, but with RAID4, the maximum disk in a RAID Group
decrease from 14 to 7. In the end, either using RAID-DP or RAID4, the
capacity is the same.

Now, why RAID5 is not supported? I believe using RAID5, I can get more
storage capacity, can't I?
I also notice with some onboard RAID controller, they only support
either RAID0, RAID1, or RAID1+0. No RAID5.

What's wrong with RAID5, is there any technical limitation with RAID5?

Thanks.