I went down that rabbit hole too when I thought it should have been idle. Turned out it was routine data integrity checks and indexing.
Ages ago Synology used to have (maybe still does) a virus scan utility based on clamav (I thiiiiiink) and it only found windows viruses I had in spam emails on my Mac backups.
I remember running a website off a RAM disk for a little while to maximize page speed and game servers. Laptop drives were slower than 5400 and it did give the site a good boost.
Very unstable system though. And so much fun.