[HowTo] test whether a USB-stick is a "fake"

Difficulty: ★★★☆☆

There are USB sticks and SD cards in circulation that are not of the specified size. Often you only notice this when you have lost data. But there is a way to test it. This is not laborious, but time-consuming!

  • Choose one of your USB sticks with USB2 or 3 (A 64GB USB stick is used in the examples below)

  • Install the f3 package from the AUR:

    pamac install f3
    
test the USB stick for the real size:

Insert the USB stick and see what kind of device ID it got. The easiest tool to use is: lsblk:

lsblk
NAME        MAJ:MIN RM    SIZE RO TYPE MOUNTPOINT
sda           8:0    0  931,5G  0 disk 
├─sda1        8:1    0    953M  0 part /boot/efi
├─sda2        8:2    0    900G  0 part /var/spool
└─sda3        8:3    0   28,1G  0 part 
sdb           8:16   0  476,9G  0 disk 
├─sdb1        8:17   0    512M  0 part 
└─sdb2        8:18   0  476,4G  0 part 
sdz           8:32   1   59,5G  0 disk 
nvme0n1     259:0    0    1,9T  0 disk 
├─nvme0n1p1 259:1    0      1G  0 part 
├─nvme0n1p2 259:2    0      1M  0 part 
├─nvme0n1p3 259:3    0    900G  0 part 
└─nvme0n1p4 259:4    0 1006,7G  0 part 

:warning: PLEASE check again that /dev/sdz is really your USB stick and not part of your Manjaro system.

  • Safely remove the device
  • Unplug
  • Plug it back in
  • Test with lsblk again!

The USB stick must have disappeared from the list!

  • Safely remove the device
  • Unplug
  • Plug it back in
  • Test with lsblk again!

The device should have reappeared. If you are not sure then stop here: If you enter the wrong device with the next command, you will wreck your whole system with one command !

Those who checked well can now test the USB stick. The USB stick will be deleted !!! (So save data that you still need beforehand)

sudo f3probe --destructive --time-ops /dev/sdz                                                                                              
F3 probe 8.0
Copyright (C) 2010 Digirati Internet LTDA.
This is free software; see the source for copying conditions.

WARNING: Probing normally takes from a few seconds to 15 minutes, but
         it can take longer. Please be patient.

Good news: The device `/dev/sdz' is the real thing

Device geometry:
	         *Usable* size: 59.53 GB (124846080 blocks)
	        Announced size: 59.53 GB (124846080 blocks)
	                Module: 64.00 GB (2^36 Bytes)
	Approximate cache size: 0.00 Byte (0 blocks), need-reset=no
	   Physical block size: 512.00 Byte (2^9 Bytes)

Probe time: 3'53"
 Operation: total time / count = avg time
      Read: 5.39s / 4816 = 1.1ms
     Write: 3'46" / 4192321 = 54us
     Reset: 0us / 1 = 0us

I hope your stick is as good as mine
Good news: The device ‘/dev/sdz’ is the real thing
And the Usable size: 59.53 GB (124846080 blocks) is as advertised

Test the stick for data security and speed
  • Use gparted to format the stick as a single partition with exfat (about 59GiB) and name “test”. The USB stick will be deleted !!! (So save data that you still need beforehand)
  • unplug,
  • plug in,
  • Mount the USB sick (the stick now is empty)
    For me, the stick ends up in /run/media/andreas/test/. You have to adapt this to your mount point.
    Now we fill the stick completely with data.

Warning:
:warning: This takes a really long time. For me it was about 2 hours with USB2 and 64 GB
:warning: Writing the stick this way will shorten the life of your USB stick through wear leveling, so don’t do it to often.

f3write /run/media/andreas/test
F3 write 8.0
Copyright (C) 2010 Digirati Internet LTDA.
This is free software; see the source for copying conditions.

Free space: 59.53 GB
Creating file 1.h2w ... OK!                           
Creating file 2.h2w ... OK!    
...
Creating file 59.h2w ... OK!                         
Creating file 60.h2w ... OK!                        
Free space: 0.00 Byte
Average writing speed: 7.75 MB/s

Now we just have to read the data again and compare. Warning: it takes a really long time. :warning: With USB2 and 64 GB it was also almost 2 hours.

f3read /run/media/andreas/test                                                                                                                            
F3 read 8.0
Copyright (C) 2010 Digirati Internet LTDA.
This is free software; see the source for copying conditions.

                  SECTORS      ok/corrupted/changed/overwritten
Validating file 1.h2w ... 2097152/        0/      0/      0
Validating file 2.h2w ... 2097152/        0/      0/      0
Validating file 3.h2w ... 2097152/        0/      0/      0
Validating file 4.h2w ... 2097152/        0/      0/      0
...
Validating file 58.h2w ... 2097152/        0/      0/      0
Validating file 59.h2w ... 2097152/        0/      0/      0
Validating file 60.h2w ... 1103104/        0/      0/      0

  Data OK: 59.53 GB (124835072 sectors)
Data LOST: 0.00 Byte (0 sectors)
	       Corrupted: 0.00 Byte (0 sectors)
	Slightly changed: 0.00 Byte (0 sectors)
	     Overwritten: 0.00 Byte (0 sectors)
Average reading speed: 12.48 MB/s

I hope your stick is as good as mine
Data LOST: 0.00 bytes (0 sectors)

Note: The full instructions for f3 can be found here

  • my USB-stick was good
  • my USB-stick had errors
  • my USB-stick is a fake (much smaller then advertised)

0 voters

1 Like