f3read

Validate a device by checking the files in a given directory

$ f3read [path/to/mount_point]

f3read [OPTION...] DEVICE

--help
    display this help and exit

--version
    output version information and exit

f3read is a utility from the F3 (Fight Flash Fraud) suite designed to test and verify the actual storage capacity of flash-based devices like USB drives, SD cards, and MMC cards. It works by reading data previously written to the device using f3write, which fills the entire claimed capacity with a specific non-compressible pattern of test data.

f3read scans the device block by block, checking for read errors, data corruption, or unexpected end-of-device conditions that reveal fake capacities. Fake drives often fail beyond their true size, simulating data or halting reads. The tool reports the largest reliable size, error locations, and overall verdict (e.g., PASS/FAIL).

This is essential for detecting counterfeit storage sold with inflated capacities, preventing data loss. Always unmount the device first and run with sufficient privileges (often sudo). f3read auto-detects f3write patterns and provides detailed stats like average speed and error rates.

Run only after f3write on the same device; unmount filesystem first; requires block device access (e.g., sudo); destructive if misused—back up data; slow on large drives.

Unmount device, then:
sudo f3write /dev/sdX
sudo f3read /dev/sdX
Replace /dev/sdX with your device (check with lsblk).

Look for 'Largest tested OK size' vs. advertised; 'FAIL' regions indicate fakes; speeds shown in MiB/s.

Developed by Roberto Pedroso as part of F3 suite around 2010 to combat rampant fake flash memory fraud; actively maintained, latest versions improve speed and compatibility with modern filesystems.

f3write(1), badblocks(8), hdparm(8)