Comment by Dwedit

Using mmap means that you need to be able to handle memory access exceptions when a disk read or write fails. Examples of disk access that fails includes reading from a file on a Wifi network drive, a USB device with a cable that suddenly loses its connection when the cable is jiggled, or even a removable USB drive where all disk reads fail after it sees one bad sector. If you're not prepared to handle a memory access exception when you access the mapped file, don't use mmap.