Scanflash

scanflash: Utility for testing flash memory devices Copyright 2012 Adam Nielsen malvineous@shikadi.net http://www.shikadi.net/scanflash/

This program writes and then verifies data on every block of a device, to ensure that the data written is exactly what is read back.

It is designed to help test for fake memory cards and USB flash drives, which often report their size to be much larger than it is in reality. Usually the start and end of these devices will hold data, so that simple tests like copying files will appear to succeed, even though the data is silently being lost. This is because the area in the middle of the devices will either lose data written to it, or it will overwrite data elsewhere on the device (which makes detection harder, as you will always be able to read the data you just wrote.)

scanflash works by writing unique codes across the entire device, and only once the whole device has been filled does it attempt to read the data back again. This allows it to detect the following types of problems:

• Black holes, where data written just disappears.

• Overlaps, where data written actually overwrites data elsewhere.

• Corruption, where data can't be read or written properly.

Rather than just identifying bad devices, scanflash will try to figure out which parts of the storage device are unusable. It will then create a special partition around the bad data, preventing it from being used. Partitions are created to provide access to the rest of the space, so that the card can still be used, albeit with a smaller capacity than what it says on its label.