I have a SQL Server 2017 instance that seems to be running a bit slowly. CPU and Memory usage looks to be normal, but disk usage might be a bit high. The data files are on disk E and the log files are on disk F. Does "Highest Active Time" pegged at 100% on the data disk indicate the need for faster drives, or to split the data files across additional disks?
Not necessarily. You should take a look at the Activity Monitor first to see what queries are running towards the database. See more here: https://docs.microsoft.com/en-us/sql/relational-databases/performance-monitor/open-activity-monitor-sql-server-management-studio?view=sql-server-2017.