The 80% "rule" hasn't been a thing for a while, but any filesystem is going to have issues with finding free blocks as it fills up... Ext used to reserve 3-5%

The 80% "rule" hasn't been a thing for a while, but any filesystem is going to have issues with finding free blocks as it fills up... Ext used to reserve 3-5% "for root", but the reality is that you're supposed to free up space if you let it get that full.