Checking USB flash drives and flash memory cards for correct functionality

Test Run

Article from Issue 161/2014

USB memory sticks and flash memory cards are part of the equipment of almost every mobile IT user today, but media defects can cause data loss. A small tool by the name of F3 helps.

USB sticks and flash memory cards are small, lightweight, and available in a variety of storage capacities, but even though they have no mechanical components, and some sticks even have a metal housing, the memory is not completely wear-free. Some flash storage media, often offered for low prices online, can fail to reach the advertised capacity. This shortcoming is really annoying when your important data is suddenly gone or you can no longer access the medium because of memory cell failure.

To spare yourself this mishap, you need only two things: Linux and the F3 program. F3 uses a read and write test to verify the integrity of the memory cells of your flash media and thus prevent unpleasant surprises.

Get Started

The program, which hails from Brazil, is available from a no-frills website as a source code archive [1]. Start by downloading the ZIP archive and unpacking it in a directory of your choice. Next, change to the newly created f3-2.2 subdirectory and compile the software in a terminal using the make linux command.

If you see an Error 127 message initially, you need to install make and the gcc collection from your distribution's repositories. When successfully compiled, the routine generates two executable programs: f3write and f3read  [2]. These two command-line tools test your flash medium with read and write accesses to determine the actual available capacity, and they help you track down defective memory cells and placebo storage quickly and reliably.


I tested the software with an Intenso stick [3] and a no-name USB stick – both of which claimed to have 4GB of capacity – as well as an SD card. To use F3, you first need to make sure you have backed up all the important data on the storage medium to be tested before emptying the medium. F3write writes 1GB files with an extension of .fff to the medium; depending on the capacity, the last file to be written can be smaller.

Because f3write does not overwrite any existing data, the medium should be completely free of old data to ensure reliable writes by f3write. To start the software, you simply enter the following command in a terminal:

./f3write /media/<drive-UUID>

Or, in distributions that use udisks2, enter:

./f3write /run/media/<username>/<drive-UUID>

The software generates the files and displays its progress in the terminal (Figure 1).

Figure 1: In the first run, F3 writes to the entire disk.

Depending on the capacity and memory blocks used, the write process can take quite a long time – even for smaller media, because they often reach their limits at speeds of 2 to 4MBps. Premium storage hardware, however, will also impress with higher write rates.

After successfully completing the write operation, enter the following in the terminal:

./f3read /media/<drive-UUID>


./f3read /run/media/<Username>/<drive-UUID>

F3read now reads the newly generated files. If any problems occur, or the tool cannot read some sectors, you will immediately see this reported in the terminal. After completing the read operation, the read speed is also visualized (Figure 2).

Figure 2: When reading this storage device, no irregularities are reported.

On the basis of the value detected when reading the storage medium, you can see the true capacity of your flash memory device. If the memory size differs compared with the capacity from the write operation and, in particular, if Corrupted shows a value other than 0, your flash memory is defective.


To test the reliability of F3 for storage media using various platforms, I formatted the test objects with different filesystems and then told F3 to read and write to the drives. I discovered that the software worked fine with USB memory sticks and memory cards using the typical FAT32 filesystem, as well as with media using the popular Linux ext2 filesystem. Additionally, F3 had no problems with the FAT16 filesystem designed for smaller disks. The write and read speeds are similar, independent of the filesystem used.

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