View your Mac’s disk activity in the Activity Monitor window or in the Dock.
To see disk activity, click Disk in the Activity Monitor window.
Activity Monitor tracks the number of times your Mac accesses the disk to read and write data, and shows the amount of data that’s read or written to your disk.
To see a graph of disk activity in the Dock, choose View > Dock Icon > Show Disk Activity.
To make more columns visible, choose View > Columns.