Is the capacity real?
Probe for fake capacity quickly, then fill and verify the available space for a thorough check. Detect drives that discard new data or overwrite earlier files.
A closer look at your storage
Know what your
drive can
really hold.
That 1 TB label only tells half the story. Check your drive’s real capacity, data integrity and speed before you trust it with your files.
Windows 10 / 11, 64-bit
Capacity checkIllustrative example
USB flash drive
Write it. Read it. Check it.
Claimed capacity128 GB
Verified in this example16 GB
Capacity mismatch detected
Claims 128 GB. Only 16 GB retains the written data.
Example results, not a live test or an app screenshot.
One executableNo installationGUI and command lineUSB, SD, SSD and HDD
Inside the toolbox
Get to know your drive.
From a suspicious bargain to an old backup drive, find out what your storage actually does with your data.
Does the data stay put?
Repeat write-and-verify passes with fresh test data. Check again after unplugging, or come back later to see whether the stored data still matches.
Where does it slow down?
See transfer speed across the drive, long stalls and slow regions. Test random 4K access and how it handles thousands of small files.
What can you show?
Save an HTML or JSON report with the drive’s identity and test results. Export a concise evidence sheet to attach to a refund request.
Your drive. Your workflow.
A window or a terminal.
The same thorough tests.
Open the app for a graphical interface, or use the command line for repeatable tests and machine-readable reports.
- Select the drive you want to check.
- Choose a quick probe or a full test.
- Read the verdict and save the evidence.
POWERSHELL
# See connected drives> flashtester list
# Write and verify free space on E:> flashtester test E:
# Save a report of the test> flashtester test E: --report result.html
Example commands. Back up your files before testing.
Before you test
A few useful details.
Will testing erase my files?
Whole-disk write tests erase the selected disk and require confirmation. File-mode tests use free space, but a fake drive can wrap writes onto existing files. Back up anything important first. The read-only surface scan does not write to the drive.
Does a quick check prove a drive is good?
A quick probe samples locations to look for fake capacity. It does not verify every byte or guarantee future reliability. Run a full write-and-verify test for more complete coverage.
Which drives can I test?
USB sticks, SD cards through a reader, external drives and secondary internal SATA or NVMe disks. FlashTester refuses disks containing Windows, boot/system partitions or a page file.
In development
A small tool for a little more certainty.
FlashTester is being built for Windows. The first public download will appear here when it’s ready.