Started a collection of 160GB HDDs from random manufacturers. The goal is the achieve 20 TB of space in a ZFS pool (RaidZ or Z2) for a media server but I'm poor and can't afford to buy all HDDs at once. I know I can't "add" HDDs to a pool, but I can replace HDDs with higher capacity drives as far as I know? So is it a problem to build a ZFS media server with 160GB disks, have it operational, and slowly replace all drives with higher capacity 3 (or 4) TB disks? Are there risks? I plan on having the OS on 2 SSDs in a mirrored Vdev. I also read about people adding a SSD in front of ZFS pools to act like a cache? Is this useful for a media server? I mean, if you always access different media then trying to store "frequently accessed files" seems kind of pointless to me. And if it acts like a buffer, I also fail to see the point for me as I'm not concerned about write speeds overall. This will be a dedicated media server box.