Difference between Partition and Erase in Disk Utility

Erase
The next pane, Erase, does exactly what you would think it should: It erases drives and partitions. This is essentially a quick-and-dirty partitioning and initialization tool; it creates a single empty partition on the selected device and erases anything that was previously there. Figure 3.58 shows the Erase pane.

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Partition
To create a more complex drive layout, use the Partition pane. Shown in Figure 3.59, this is the control center for working with your drive. Be warned—changes here will erase any information on the target drive!

The Volume Scheme section of the Partition pane contains a visual representation of the partitions on the system. Each box is a partition. The highlighted box is the active partition.

You can change a partition's size by dragging the dividers between the partitions up and down to shrink or grow the available space. As you drag the bar, the size field on the right portion of the pane changes to show the current settings.

Figure 3.59 Partitioning your drive erases any existing information.

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Difference: ERASE erases a volume, PARTITION partitions an external HDD into several partitions, this data already on that drive might get deleted..

 

In either case... before you do anything to your drive(s), always make sure you have an up to date backup strategy