1.) So, some people, such as the person in this article: https://www.howtogeek.com/324956/how-much-free-space-should-you-leave-on-your-windows-pc/ Are suggesting 15% free space for a mechanical hard drive defrag. However, I believe I've heard others say this practice has been irrelevant since Windows Visa, and depending on who I talk to, a little over 200 MB to a few GB is enough to defrag a mechanical hard drive. My OS isn't installed on this HDD, just self-created media files ranging from 4 GB to 80 GB. It's a high-use 10 TB HDD. So 15% of that would be 1.5 terabytes. That's an insane amount of storage space I'd be giving up if this were true. But some are saying if It's not 15-20% free, the HDD will work a lot harder, be slower and the risk of failure will go up. And I guess Microsoft's own documentation says 15% https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/defrag But still, giving up 1.5 terabytes seems kinda insane. So what should I do? 2.) If I recall correctly, MS automatically defrags internal HDDs via the "Optimize Drives" application? My "Scheduled Optimization" is "On" so if I have less than 15% free space, that could cause a problem?