Fake SD Card & USB Drive Test (Real Capacity and Speed)

About the Fake SD Card & USB Drive Test (Real Capacity and Speed)

Fake memory cards and pen drives report a capacity they do not have: a “1 TB” stick may hold 32 GB and quietly write anything beyond that over earlier data. This test finds out. It fills the card’s free space with test files in which every 512-byte sector says which test and which position it belongs to; you then unplug the card and plug it back in, and the page reads every sector back and compares it.

The result says how much came back correctly, where data starts to come back wrong (the card’s real usable space), whether sectors were written over by others (the mark of a fake) or came back with flipped bits (a failing card), and the approximate write and read speeds. It runs in Chrome or Edge on a computer, which can write into a folder you choose; nothing is uploaded.

Common uses

• Checking a card or pen drive bought online before trusting it with photos or backups.
• Finding the real usable size of a suspicious “high capacity” stick.
• Testing a card that lost files or showed errors in a camera, drone or dashcam.

How fake cards are caught

A fake card’s controller reports a large capacity but has a small flash chip, so writes beyond the chip’s size land on space that already holds data. A test that writes data it can recognise everywhere, then reads it all back, sees it: sectors come back holding another position’s data, or garbage. Because every sector of the test says its own position, the page can tell written over (another position’s test data: the mark of a fake), damaged (anything else) and bits flipped (in place, a few bits wrong: a failing card) apart.

This is the method of the free, open-source F3 (Fight Flash Fraud), written again from scratch for the browser; MySmartCoPilot is not affiliated with F3.

Why you unplug the card between writing and checking

Right after writing, the computer’s file cache can still hold the test data and hand it back without reading the card, and some fake cards keep the last few hundred megabytes in a cache of their own: a test that reads at once can let a fake card pass. F3’s documentation gives the same advice: disconnect and reconnect the device before reading (F3 usage notes). A web page cannot empty those caches itself, so the page asks you to reconnect the card and choose its folder again.

About the speeds

The write and read speeds are measured at file level, as the browser writes and reads the test files. The operating system buffers writes, so short tests show more than the card sustains, and the speed also depends on the card reader and the USB port. They are a rough check, not a benchmark.

Limitations

• Needs a browser that can write into a folder you choose: Chrome or Edge on a computer. Firefox and Safari cannot.
• Only the free space is tested; the files already on the card are not read.
• It cannot repair a fake card or set its real size: that needs low-level access no web page has. A fake card is best returned; if you must use it, keep its data below the point where data went wrong.
• Filling a large card takes as long as writing that much data: hours for 256 GB on a slow card.

Privacy

Everything happens between your browser and the folder you choose: the test files are generated in the page and read back there. Nothing is uploaded.