The Quick Size Test is the mode most people mean when they talk about FakeFlashTest, and its marker blocks are the whole idea. This guide explains exactly what the test does, why it destroys data, how long it can honestly take, and how to run it without making the classic mistakes. If you want the full start-to-finish routine for a new drive, read it alongside our main guide on how to test a USB flash drive for fake capacity.
FakeFlashTest is a freeware, Windows-only, portable tool by Steve Si. Get it from the official source via our download page. The latest version, v1.1.5, is described by the developer as the latest Beta build. There is no install: you extract the password-protected ZIP (the extraction password is fake) and run the program.
What the Quick Size Test actually does
The test writes small marker blocks — 512 bytes each — at intervals spread across the drive, and then reads them back to check that each marker is still intact at the address where it was written. It starts from the end of the reported capacity and works through the drive, which is a deliberate choice: a fake drive lies most obviously at its far end, where the reported space does not exist at all.
On a genuine drive, every marker can be written and read back correctly, because every reported sector corresponds to real flash memory. On a fake drive, the controller reports far more capacity than the physical chip holds. Markers written beyond the real capacity either fail, overwrite earlier markers as the addresses wrap around, or read back corrupted. Any of those outcomes exposes the lie quickly, without filling the entire drive byte by byte.
That sampling is also the test’s limit, and the developer states it plainly: FakeFlashTest is a quick screen. It does not thoroughly test all of the memory and it does not check for faults everywhere. A drive can pass the Quick Size Test and still have a defective area between two sampled points. For a thorough verdict you need a full write-and-verify test such as H2testw, which can take hours. Think of the Quick test as a fast, usually decisive capacity check — not a complete health certificate.
Warning: this test is destructive
The Quick Size Test destroys the data on the selected drive. Writing marker blocks across the drive overwrites file system structures and file data, and afterwards the drive will normally need to be formatted before reuse. Never run it on a drive that holds the only copy of anything.
Back up first, verify the backup opens, and then double-check the drive letter inside FakeFlashTest against the letter in File Explorer. Selecting the wrong letter is the most damaging mistake a user can make with any destructive test, and it is entirely preventable with ten seconds of care. If you cannot empty the drive, do not use this mode — use the preserving alternative described in our Test Empty Space guide instead, and accept that it only tests free space.
How to run it, step by step
First, connect the drive directly to the computer, avoiding hubs where possible, and confirm Windows shows it with a drive letter. Second, right-click FakeFlashTest and Run as Administrator — without administrator rights the tool will not list USB drives at all. Third, select the correct drive in the tool, reading its letter and size twice. Fourth, choose Quick Size Test and start it, then leave the computer to work: do not remove the drive, let the PC sleep, or hammer the machine with other heavy disk activity while the test runs.
Finally, let the test reach its own conclusion and read the full log, not just the headline. Our guide on how to read FakeFlashTest results explains what passes, failures, and real-capacity figures mean, and why screenshotting the log matters if you need a refund.
How long should it take? Honest timing
The developer’s own example diagnosed a fake 16 GB drive in 27 seconds. That example is real, and it shows why the test is called Quick — but it is a single example on a small fake, never a guarantee for your drive. Timing depends on the reported capacity, the real speed of the device and reader, and how the controller behaves once writes pass its real limit.
A small genuine drive may finish quickly. A drive claiming a very large capacity, a slow card in a slow reader, or a fake whose controller struggles under sustained writes can take much longer — potentially far longer than a minute or two. Judge progress by whether the test is advancing, not by a stopwatch. If it appears completely frozen for a very long time, consult the troubleshooting advice for stuck tests rather than repeatedly unplugging the drive mid-write.
If the Quick test fails every drive you try
There is one result that should make you suspect your computer rather than your drives: the Quick Size Test failing every drive, including one you know is genuine. The developer addresses this directly — security software or a driver interfering with the tool’s low-level access is the usual cause, and the advised fix is to run FakeFlashTest in Windows Safe Mode, where that interfering software is not loaded.
That scenario has its own dedicated guide: Quick Size Test Fails Every Drive? The Safe Mode Fix. Follow it before concluding that several unrelated drives all happen to be fake. Testing a known-good drive alongside a suspect drive, on the same PC and setup, is the simplest sanity check in this whole subject.
Used as intended — empty or backed-up drive, administrator rights, correct letter, patience, and a careful reading of the log — the Quick Size Test is the fastest honest answer to the only question that matters on day one: is this drive’s capacity real? Download the tool from the download page, run it on arrival, and you will know before your files are at risk.