Monitoring Disks

Disks: Introduction

System Monitor can monitor the current performance values for disks currently connected to your computer. The current sums of the read and written data of all selected disks are displayed in the menu bar in this case. The term disks should denote all objects which identify themselves to the computer as being block-oriented storage devices. Next to hard drives, this includes optical disks, floppy drives, or storage card readers, for example.

If you like to monitor disks of your computer, perform the following steps:

1. Ensure the control window of System Monitor is open.
2. Select the item Information Sources > Disks in the sidebar.
3. Make sure the check mark Monitor this item is set at the right side of the window.

Only those disks will become part of the statistics which you have selected for monitoring (see below).

The data shown is calculated live and updated about once per second.

Disks: Menu Bar

The box Menu Bar controls in which form disk performance should be displayed. System Monitor offers a variety of icons and functions that you can combine in any order. The following elements can be used:

• The label HD (hard disk) in small, vertical print to designate disk performance values and to separate them from other icons in the menu bar.
• The label HD in large, horizontal print.
• The display of read (R) and write (W) data transfer rate as plain text in two lines using small print.
• The display of read and write performance history for the last 30 seconds.
• A spacer to put more room between items.

Within the box, the upper bar simulates as a sample how this monitor section should be presented in the menu bar. You can grab the individual items by mouse and move them into a different order. You can remove an element by pulling it out of the bar. The lower bar contains the stock of items available. If you like to add a certain item to the menu bar, use the mouse to drag it from the lower to the upper bar. Pressing the button Default causes your current settings to be deleted, replacing it by a default suggestion for the menu bar.

Spacers are shown with dotted rectangles to make it easier for you to recognize and to move them. In the actual display, the rectangle will become invisible, so the spacer does its job providing a blank area within the menu bar.

If you mistakenly have removed all items of this monitoring section from the menu bar, a three-star-icon (⁂, asterism) will appear as a placeholder. This ensures that you still can open the associated menu.

You cannot drag items directly into the real menu bar.

Disks: Menu Items

At least the following items will be shown for each selected disk as part of the menu associated with this monitor section:

• The name of the disk according to its vendor. If available, the serial number will also be shown in parentheses.
• An additional comment line which Macintosh volumes are located on this disk. This is helpful to relate the activity on disks to the disks’ volumes, in particular if you have multiple hard drives of the same model type. This line can be empty if a disk does not contain any readable volumes, or if the file systems of the volumes don’t have valid Macintosh names. For technical reasons, the names will appear with a delay of one minute after launching the App.
• A combined history graph showing read and written data for the last 30 seconds.
• Read Throughput: the current data transfer rate for read operations within the last second.
• Write Throughput: the current data transfer rate for write operations within the last second.
• Reads: the current rate of read operations within the last second.
• Writes: the current rate of write operations within the last second.
• Peak value (read): the peak value of the read data rate observed since the start of System Monitor.
• Peak value (write): the peak value of the write data rate observed since the start of System Monitor.
• Read Data: the total amount of data read since the operating system was started.
• Written Data: the total amount of data written since the operating system was started.
• Reads: the total number of read operations since the operating system was started.
• Writes: the total number of write operations since the operating system was started.

Disks: Displaying history graphs

The history graph in the menu bar and the individual history graphs in the menu can be shown in different modes of operation. The following options can be set:

Display Style: If you select Back and Front, the read data rate will be displayed dark at the back, the write data rate will be displayed lighter in front. If you switch to Opposed, the read data rate will be displayed in the lower half of the graphics, growing from bottom upwards, the write data rate will be displayed in the upper half of the graphics upside down, growing from top downwards.

Automatic Zoom: The history will automatically focus on the value range observed in the presented 30 seconds. The curve will always be magnified to make the graph cover a certain area. In the mode Scale to peak since start, the curve will be magnified to a degree that the maximum of the curve will match the maximum of values System Monitor has observed so far. This is the “most honest” mode of operation: If the monitored values have found their level after some time, the peak in the graph will match the peak performance the monitored disk can provide. Small data transfer rates, however, can become invisible because they might be so small compared to the peak value that they can no longer be represented graphically. The alternative is the setting Magnify displayed interval. Here, the zoom factor will be tuned each second, attempting to always make the smallest details found in the last 30 seconds visible. However, the magnification can now switch back and forth unpredictably, with small changes leading to an exaggerated impression. Both settings have their advantages and disadvantages.

Selecting the disks to monitor

The table Include the following disks allows you to control which drives should be monitored by the app and which shouldn’t. Set a check mark next to each disk which should be monitored and remove the check marks for disks where no monitoring should be performed. The selection can also be applied to all entries automatically, using the buttons All or None. The lines in the table can be dragged to a different sort order if desired. This order will then be used for the corresponding sections in the menu.