Storage speed collapses mid-benchmark? What to test

Your storage test starts quickly, then the speed drops sharply before it finishes. That can point to a real slowdown, but one dip does not prove the drive is failing. Background activity, heat, available space, and the type of work being measured can all affect the result.

Use the Storage Test to compare large-file speed with small-write speed, then repeat the test under steady conditions. These checks can help narrow down the cause, though a browser benchmark cannot inspect every part of a drive or confirm its health.

Repeat the storage test fairly

1. Open the Storage Test and run it once. Note whether the slowdown happens during large-file testing, small writes, or both.
2. Close file transfers, game downloads, cloud sync, and other busy apps. Wait a minute or two so the drive and computer can settle.
3. Run the same test once more without changing the drive, connection, or other conditions. If you are using a laptop, keep it plugged in and on a firm surface.
4. Compare the results. A similar drop in both runs is more useful evidence than a single unusual result. Write down which part of the test slowed and whether the whole computer also felt sluggish.

Avoid running many benchmarks back to back. Repeated work can heat the drive or keep other system activity busy, making later results harder to compare. For help understanding the different result types, see How to interpret storage test read and write speeds.

What the result means

Speed drops in both runs

A repeatable drop suggests a limit that persists under those conditions. It may be heat, background disk activity, a nearly full drive, a slow connection, or the drive's normal behavior during sustained work. Check those factors before treating the result as a fault.

Only the first run drops

The computer may have been busy with updates, indexing, a download, or file syncing during that run. A one-off dip can also happen when the operating system is handling other work. Repeat after the computer has been idle rather than relying on the first result.

Large-file speed falls, but small-write speed stays steadier

The drive may handle short writes differently from a longer stream of data. Some solid-state drives use a fast temporary write area, then slow down after it fills. That behavior can be normal, especially during sustained writing. A browser test can show a change in speed, but it cannot identify the drive's internal cache or prove why the change occurred.

Small writes are slow from the start

Small writes involve many separate operations, so they can be slower than transferring one large file. Background file activity or a connection through a hub can also affect them. Compare like with like, and do not treat a small-write result as the same thing as copying a single large video file.

The result changes a lot between runs

Unsteady system activity, temperature, power settings, and the connection can all cause variation. If the computer is otherwise responsive and the drive works normally in everyday use, variable browser results alone are not enough to diagnose a failing drive. A browser file test also cannot measure every storage operation, such as all forms of random access. See What a browser file test can't measure about IOPS for that limitation.

How to fix or narrow it down

1. Stop other disk activity. Pause large downloads, backups, game updates, and cloud synchronization before testing. On Windows 11, open Task Manager with Ctrl + Shift + Esc and check which apps are using the disk. On macOS, open Activity Monitor and select the Disk view.
2. Check available space. Keep some free space available for the operating system and temporary work. On Windows 11, open Settings › System › Storage. On macOS, open System Settings › General › Storage. Free space if the drive is nearly full, then test again.
3. Keep the computer cool. Place a laptop on a hard surface so its vents are not blocked. If the drive or computer feels unusually hot, stop testing and let it cool. A hot drive can reduce speed to control temperature.
4. Check the power mode. Connect a laptop to power for the comparison. On Windows 11, check Settings › System › Power & battery and review Power mode. On macOS, check System Settings › Battery for Low Power Mode or other power options that may affect performance.
5. Reconnect an external drive safely. Eject it through the operating system before unplugging it. Then connect it directly to another suitable port, rather than through a hub or splitter, and repeat the test. A different cable or port can help identify a connection bottleneck.
6. Restart and retest once. A restart can clear a stuck transfer or background task. After signing in, let startup activity finish before running the test again.

When the drive may need attention

Take a repeated slowdown more seriously if it comes with read or write errors, files that will not open, frequent disconnects, or the computer freezing during ordinary file use. Back up important files before doing more tests. A browser benchmark cannot check a drive's health records or guarantee that stored files are safe.

If the same drive also fails or disconnects on another computer, check its cable and enclosure if it is external. If the problem remains, contact the manufacturer or a repair professional, especially while the drive is under warranty. Avoid repeatedly stressing a drive that is already making files inaccessible.

Why a benchmark can slow down partway through

A short burst and a sustained workload are not the same thing. A drive may write quickly at first, then slow when a temporary buffer fills or when heat builds up. The operating system may also start another task during the test. These effects can change a benchmark without showing that the drive has suddenly become defective.

For a useful comparison, change one condition at a time: first close background apps, then try a direct connection, or compare after the drive has cooled. That makes it easier to see which change affects the result.