It works!

20 (16)TB of hard disk space:

Balance on '/data' is running
289 out of about 432 chunks balanced (290 considered), 33% left
Label: none uuid: 5fb8255b-5201-44af-8712-6c8dff56f033
 Total devices 5 FS bytes used 666.82GiB
 devid 1 size 3.64TiB used 425.01GiB path /dev/sde1
 devid 2 size 3.64TiB used 425.01GiB path /dev/sdc1
 devid 3 size 3.64TiB used 288.00GiB path /dev/sdg1
 devid 4 size 3.64TiB used 288.00GiB path /dev/sdd1
 devid 5 size 3.64TiB used 288.00GiB path /dev/sdf1

Data, RAID0: total=270.00GiB, used=258.90GiB
Data, RAID5: total=1.12TiB, used=406.78GiB
System, RAID1: total=8.00MiB, used=128.00KiB
Metadata, RAID1: total=2.00GiB, used=1.14GiB
GlobalReserve, single: total=512.00MiB, used=0.00B

Coming up next: automatically scaling wordpress cluster (not that I’m going to ever need it)…