How are you using plex? If you're using a web browser on a pc I would switch to the app. Plex isn't exactly reliable at all IMO, using the app on pc solved a lot of problems for me.
Data Hoarder
We are digital librarians. Among us are represented the various reasons to keep data -- legal requirements, competitive requirements, uncertainty of permanence of cloud services, distaste for transmitting your data externally (e.g. government or corporate espionage), cultural and familial archivists, internet collapse preppers, and people who do it themselves so they're sure it's done right. Everyone has their reasons for curating the data they have decided to keep (either forever or For A Damn Long Time (tm) ). Along the way we have sought out like-minded individuals to exchange strategies, war stories, and cautionary tales of failures.
How are you using plex? If you're using a web browser on a pc I would switch to the app. Plex isn't exactly reliable at all IMO, using the app on pc solved a lot of problems for me.
Are you seeing high IOWait? How did you determine that it's an IO issue?
I can download/write + stream to multiple users off a HDD that's MUCH slower than your SSD without any issues, so I suspect something else is going on.
Will a HDD work for my purposes?
HDDs are much slower than an SSD, like more than 30,000x slower on IOPS.