I have a few questions about Western Digital 10 TB Red & Seagate Ironwolf 10 TB HDD's. 1.) I currently use some of these drives in my Windows desktop PC. I'm wondering how much overhead (free storage space) I should leave to keep the read/writes running optimally and also so Windows can defrag them. This seems to be a highly controversial subject for some reason. I've seen people/articles suggest 15-20% for Windows Defrag. Others claim this is an outdated estimate and instead suggest 5% or even lower. Does anyone know for sure? 2.) I'll eventually be moving these drives over to my Synology DS918+ NAS and using RAID 5 or SHR-1 and the same question as above applies. If I want to keep the read & writes running optimally and if I want to keep them defragged via whatever software solution Synology uses, how much free space should I leave available? The reason I'm asking these questions is because I have enough data to 'top off' these drives and then some, but I don't want to do it at the expense of performance/HDD longevity/the proper functioning of Windows/Synology defrag.