EX 3200/4200 switches (I've not personally checked other models) allow the entire device to be operated from a USB key installed in the external USB slot. Additionally the internal flash can be snapshot to an external USB flash device as a backup measure.
For example I have a customer running all their EX Switches from External USB flash drives.....they have some backup/spare EX4200's in storage pre-configured to operate from the USB slot. So during a failure event they take one of the shelf, move the USB over an power it on. This is great for installations where you don't have experienced network engineers :)
Francois
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