How to test storage speed after a power failure

A power outage, sudden shutdown, or failed power supply can leave you wondering whether your drive is slower or damaged. A speed check can show whether its performance has changed, but it cannot tell you whether your files are safe or diagnose every kind of drive failure.

Start by protecting important files, then use the Storage Test to check large-file speed and small writes. If the drive is making unusual noises, disconnecting, or showing read errors, skip the test for now and focus on saving your data.

Check storage speed safely

1. Open the Storage Test. If the drive is unstable or contains the only copy of important files, do not run a test yet. Back up the files first, if you can read them reliably.
2. Check that the drive appears normally in your computer and that it is connected securely. For an external drive, use its usual cable and connect it directly to the computer rather than through a hub.
3. Close file transfers and apps that are using the drive. Keep the computer connected to reliable power, especially if you are testing a laptop.
4. Run the test once and let it finish. It measures large-file disk speed and small-write performance. Avoid running other storage tests at the same time.
5. Note the results and compare them with a previous result from the same drive, if you have one. If the first test looks unusually slow but the drive seems stable, close other apps and repeat it once under the same conditions.

A score is most useful as a comparison with that drive's own earlier results. Different drives and computers can have very different speeds, so a score alone does not prove that a drive is healthy or faulty.

What the result means

Speed is close to your earlier result

The power event may not have changed the drive's measured performance. This is reassuring, but it does not rule out file-system errors or damage that has not affected speed. Keep a separate backup and check that important files open.

Large-file speed looks normal, but small writes are slow

Small writes can be affected by background activity, free space, encryption, and the drive's own design. Close apps that may be writing to the drive and check again. A weak result is a reason to investigate, not proof of a failing drive.

Both results are much slower than before

Check the cable, port, power supply, and available space before blaming the drive. If the same slowdown persists with a stable connection and little background activity, back up your files and check the drive for errors.

The test stalls, the drive disappears, or files show errors

Stop testing. Repeated reads and writes are not a repair, and continued use may make recovery harder if the drive is failing. Copy essential files only if the drive remains accessible and does not repeatedly disconnect. If the data is irreplaceable, ask a data recovery professional before trying repairs.

What to do after the test

1. Back up important files. Copy irreplaceable files to a separate drive or trusted backup location before running repair tools. Do not treat a second partition on the same physical drive as a backup.
2. Check the connection and power. For an external drive, try another cable or port, and connect it directly to the computer. If it uses a separate power adapter, check that the adapter is firmly connected and is the correct one for the drive.
3. Check available space. A nearly full drive can behave differently from one with room to work. On Windows 11, open Settings › System › Storage. On macOS, open System Settings › General › Storage to check the startup disk. Remove only files you have backed up or no longer need.
4. Restart after your files are safe. A normal restart can clear a temporary system or connection problem. Do not repeatedly force the computer off while it is writing files.
5. Check the file system. Back up first. In Windows 11, open File Explorer, choose This PC, right-click the drive, select Properties › Tools, then use Error checking. On macOS, open Disk Utility, choose View › Show All Devices, select the volume, and run First Aid. Follow any on-screen instructions, and do not interrupt the check.
6. Compare results again only if the drive is stable. Run the Storage Test once more after the connection and system checks. If it remains slow or errors return, stop using the drive for routine work and arrange a proper diagnosis.

When the drive may be failing

Take repeated warnings seriously if the drive vanishes, takes a long time to open files, produces read errors, or causes the computer to freeze during access. A hard drive may also click, grind, or repeatedly spin up and stop. SSDs do not make the same mechanical sounds, so silence does not rule out a problem.

If a drive is under warranty, contact the manufacturer after backing up what you can. A failing internal drive may need replacement by a repair shop. If you cannot access important files and have no backup, avoid running repeated benchmarks or repair attempts. A recovery specialist can advise whether further use is likely to make recovery harder.

What a browser speed test cannot diagnose

The Storage Test checks performance in the browser. It does not read the drive's internal health records, confirm that every file is intact, or recover damaged data. Browser storage tests also do not measure every detail of disk behavior, including all small-operation patterns. For more on that limit, see what a browser file test can't measure about IOPS.

If the drive has become unreliable since the power event, make a backup the priority, even if its speed result looks normal.