The 2 tabs give physical and logical usage. The difference is physical counters will contain the sum of all logical partitions on the drive.
Logical counters will only show values for the logical partition and not for the entire disk.
IO usage is displayed per attached drive. Each drive has its own set of graphs:
IOs sec - IO operations performed per second
Bytes Sec - Bytes transfered through IO per second
Avg IO Latency (ms) - Average time that it takes to complete a single I/O operation
Avg Bytes Per IO - (Bytes per second / IOs second)
% Disk Time - the % of the disks time being used (this may go over 100% owing to the way windows sums multiple operations in the same sample interval)
Disk Queue Length - the number of processes that are waiting to use the hard disk
Not Connecting To Performance Monitor
MiniDBA is dependent on conncting to the SQL Server's built in performance monitor counters. If the it says it is unable to connect then this screen will not have sample data available.
To troubleshoot perfmon connectivity visit this link