Comment by magicalhippo

What are the errors? I tried to show exactly what you talk about.

edit: ok, I didn't consider the exact locations of the parity, I was only concerned with space usage.

The 8 data blocks need three stripes on a 3+2 RAID-Z2 setup both pre and post expansion, the last being a partial stripe, but when written in the 4+2 setup only needs 2 full stripes, leading to more total free space.