f3probe false negative

[ElonSatoshi]

I bought some USB-A + USB-C drive from a discount store that sells random junk including scam flash drives. It said SanDisk on it so I took a chance, even though I knew scammers can print the name of a reputable brand on the drive.

The whole is the same width as the USB-A male port. I looked at it, and my heart sunk when it said 1 TB. There's no way this disk could hold 1 TB.

I ran f3probe on it to see what the real size was. It was taking a long time, so I just let it run in the background.

Later I come back and f3probe claims it holds the entire 1 TB!

I stared at my screen and shouted "Bullshit!" several times.

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.

Probe finished, recovering blocks... Done

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

Device geometry:
	         *Usable* size: 931.88 GB (1954283520 blocks)
	        Announced size: 931.88 GB (1954283520 blocks)
	                Module: 1.00 TB (2^40 Bytes)
	Approximate cache size: 0.00 Byte (0 blocks), need-reset=no
	   Physical block size: 512.00 Byte (2^9 Bytes)

Probe time: 19'25"
 Operation: total time / count = avg time
      Read: 59.73s / 4197141 = 14us
     Write: 18'24" / 4192321 = 263us
     Reset: 0us / 1 = 0us

How did this drive fool f3?

[ElonSatoshi]

I found similar issue #219 and I'm running f3write on it

[AltraMayor]

Once you post the outputs of f3write and f3read on the drive, I can make an educated guess as to how the drive is fooling f3probe.

[ElonSatoshi]

Well, using those tools, I confirmed that the USB drive can hold at least 256 GB of data with no loss.

I'm actually thinking this USB drive is genuine now.

It seems likely that I got my hands on a genuine Sandisk 1TB USB-C drive. It has this serial code SDDDC3 on it, which also applies to other sizes of the same type of device. https://www.amazon.com/SanDisk-Ultra-Drive-Type-C-Flash/dp/B0CKJB51M8