2x Spare SSDs in server

The controller card for the 7x 8TB pool. Is it flashed to ‘IT Mode’ or is it a plain HBA adapter? What is the model of the controller? Are you using Mirrors or Raid-Z(1,2,3) for the pools?

BASICS

iX Systems pool layout whitepaper
https://www.truenas.com/solution-guides/#TrueNAS-PDF-zfs-storage-pool-layout/11/
Special VDEV (sVDEV) Planning, Sizing, and Considerations