How to inspect a USB drive after changing its file system

After changing a USB drive's file system, you may want to know whether the format took effect, your files still work, and the drive is performing normally. Formatting usually erases the drive, so first make sure you have a separate copy of anything you need.

You can check the format in your computer's file details, try reading and writing files, then measure the drive's real transfer speed with the USB & SD Speed Test. These checks reveal different things, so do not treat a speed result as proof that every file or part of the drive is healthy.

Inspect the drive after changing its file system

1. Open the USB & SD Speed Test. Connect the drive directly to your computer if possible, and follow the on-screen instructions to select it. If the browser asks for access to the drive, choose the drive you intend to test.
2. Confirm the format in your operating system. On Windows 11, open File Explorer › This PC, right-click the drive and choose Properties. Look for the file system on the General tab. On macOS, open Disk Utility, select the volume in the sidebar and check its information for the format.
3. Check that the drive has the format you chose, such as exFAT, FAT32 or NTFS. Make sure you have selected the USB drive, not your computer's internal disk or another connected device.
4. Copy a few nonessential files onto the drive, then open them from the drive. Copy them back to the computer as well. Try one small file and, if you regularly use large files, a larger file that fits the drive and the format.
5. Run the speed test's read and write measurements. Close file transfers and other programs using the drive first. Note the results and repeat the test once under the same conditions if the numbers seem unusual.

Do not unplug the drive while it is being tested or while files are copying. When the checks are done, eject it using your operating system before removing it.

What the result means

The computer shows the format you selected

The format change took effect on the volume you checked. This does not prove that every device you plan to use supports that format. For example, FAT32 works with many older devices but limits a single file to about 4 GB. exFAT is commonly used for large files across computers, while NTFS is most closely associated with Windows. Check the requirements of any camera, TV, game console or other device that will use the drive.

Files copy in both directions and open correctly

The drive can handle basic reading and writing from this computer. This is a useful practical check, but it does not verify every sector or guarantee that the drive will keep working over time. Keep another copy of important files.

The speed is lower than you expected

That alone does not mean the format change failed. Results vary with the drive, its connection, the computer and the size of the data being transferred. A USB hub, a slower port, background file activity or a nearly full drive can also affect a measurement. Compare results under similar conditions rather than expecting the speed printed on the drive's packaging.

The test or file copy stops with an error

The drive may be disconnected, busy, short on free space or having a problem writing or reading data. Try a different port and repeat the file check. If the same errors appear on another computer, do not rely on the drive for important files.

A large file will not copy

Check the file system before assuming the drive is faulty. FAT32 has a per-file limit of about 4 GB, even when the drive has plenty of free space. If you need to store larger files, choose a format supported by the devices that will use the drive, and back up its contents before formatting it again.

How to fix problems after the format change

1. Stop other activity on the drive. Close file transfers, backup programs and apps that may be scanning or using the drive. Wait until activity stops, then run the speed test and copy check again.
2. Check the connection. Plug the drive into another USB port, preferably one directly on the computer instead of a hub. If you use an adapter, try another compatible adapter or connect the drive to a second computer.
3. Check the selected volume and format. In Windows 11, use File Explorer › This PC › Properties to confirm the drive letter and file system. In macOS, open Applications › Utilities › Disk Utility, select the volume and check its information. A drive can contain more than one volume, so verify the one you actually use.
4. Choose a compatible format only if needed. If a device cannot use the current format, back up the drive, then format it for the devices you plan to use. In Windows 11, right-click the drive in File Explorer › This PC and choose Format. On macOS, use Disk Utility, select the correct volume and choose Erase. Formatting erases data, so check the selected drive carefully before confirming.
5. Eject and reconnect the drive. Use the eject option in File Explorer on Windows or the eject icon next to the drive in Finder on macOS. Reconnect it and repeat the read, write and speed checks.
6. Test on another computer. If errors continue, this helps separate a problem with the drive from one with a USB port, adapter or computer setting. Do not keep copying valuable data to a drive that produces repeated errors.

When the drive may be faulty

Suspect a hardware problem if the drive disconnects repeatedly, fails to complete writes, or produces read errors on more than one computer and port. Back up any files you can still read. If the drive is new and still under warranty, contact the seller or manufacturer about a replacement. For an older or inexpensive flash drive, replacing it is usually safer than trusting it with important data.

What a speed test can and cannot confirm

The USB & SD Speed Test measures read and write performance. It does not tell you which file system is installed, check whether a TV or console supports that format, or prove that the drive's full advertised capacity is usable. Use the operating system's drive information to check the format, and test with the kinds of files and devices you actually plan to use.

Keep a second copy of important files until the drive has passed your checks and worked reliably in its intended device.