Test Empty Space is the mode you choose specifically to protect files already on a drive — so an error in this mode, of all modes, deserves a careful reading. What does the error actually mean? Are the files you were protecting now at risk? And how do you get a verdict you can trust without gambling the data? This guide answers those questions in order.
For the mode’s normal behaviour, read our explainer on FakeFlashTest Test Empty Space first; for how to interpret results generally, see how to read FakeFlashTest results. The tool is obtained via the download page, and it must be run as administrator or it will not list your drive.
What Test Empty Space errors mean
Recall how the mode works: it writes test files only into the drive’s free space and reads them back, verifying at intervals as it fills — checks at points such as 3, 5, 9, and 17 GB rather than only at the end. An error means a test file that was written into free space could not be read back correctly. The drive failed to store, in its supposedly empty region, data it accepted minutes earlier.
On a fake drive, that failure has a precise implication: cumulative writes have reached, or the free-space writes have crossed, the boundary of the real chip, and the controller’s wrap-around behaviour has begun overwriting data — starting with whatever occupies the oldest addresses, which may include your test files and may include the early parts of the volume where your existing files live. On a genuine but ageing drive, the same symptom can instead indicate failing flash in the free region. Either way, the meaning is not “the test glitched.” It is “this drive did not reliably store data in the space it claimed was free,” which is exactly the question the test exists to ask.
Why files already on the drive can be corrupted
Test Empty Space is designed to preserve existing files: it writes only where the file system reports free space. That design is real, and on a genuine drive it holds. The exception is built into what a fake is. Files already on a fake drive may sit, wholly or partly, in bad areas — regions beyond the real capacity, where their contents were already wrapped, overwritten, or stored only as directory entries pointing at reused space. Such files were not protected by any test mode, because the damage mechanism is the drive’s own firmware, operating whenever writes occur, including the ordinary writes you did before any test.
This is why the guidance attached to this mode has always been “designed to preserve — but back up first.” The backup is not a formality. It is the only protection that survives the scenario where the drive’s free-space errors turn out to be the visible edge of corruption already present in your data. If you ran the test without a backup and got errors, your next action is not another test; it is the salvage in the next section.
Immediate steps after errors: protect first, test later
Stop writing to the drive. Do not save anything further to it, do not reorganise its folders, and do not re-run any test yet. Copy its existing files to your computer — copies, verified by opening them on the computer afterwards — prioritising irreplaceable files and, among them, the most recent, which are the likeliest to have survived intact if wrap-around is the cause. Work through the drive methodically and note which files verify clean and which are corrupt; that inventory is the truth about what the drive has done to your data, and no subsequent test result will improve it.
If important files are among the corrupt or missing, keep expectations honest about recovery: software can sometimes recover deleted or formatted files that have not been overwritten, but data overwritten by wrap-around is gone in substance. Our guide on what to do next after a fake is confirmed covers that salvage-and-recovery sequence in full. Only when the data is as safe as it can be made should you think about verdicts and refunds.
Getting a cleaner verdict: empty drive, Quick test
Test Empty Space, by construction, only ever tests the free portion of a drive, and its errors leave room for argument about occupied regions. Once your files are safely copied off, remove that ambiguity: with the drive empty (or content to lose its contents), run the Quick Size Test, which samples the entire reported capacity with its marker blocks, including the far end where fakes are most exposed. That complete, clean run is the verdict to screenshot and to use as evidence — a full-capacity result, on an empty drive, on a known setup.
Screenshot the Quick result log and proceed as with any confirmed fake: stop trusting the drive, claim via the platform with real-versus-advertised capacity documented, and replace through a genuine channel. If, contrary to expectations, the emptied drive passes the Quick test cleanly and the earlier errors were confined to a troubled free region of an otherwise genuine drive, you still own a drive that produced storage errors — retire it from important duty regardless. Errors are information either way. Protect the files first, then let the clean test on the empty drive, using the tool from the download page, have the final word, clearly and on the record.