External drive through a USB splitter: what to test

Your external drive works when plugged into a USB splitter, but copies are slow, transfers pause, or the drive disconnects. A splitter, usually a USB hub, can share bandwidth between devices or fail to provide enough power for a drive.

Compare the same drive through the splitter and directly through the computer, changing only one thing at a time. The USB & SD Speed Test can help with USB flash drives and memory cards. External hard drives and SSDs may not be supported by that test, so use a consistent file copy to compare those drives instead.

Compare the splitter with a direct port

Open the USB & SD Speed Test if you are testing a flash drive or memory card. Follow the test's prompts if your drive is available. For an external hard drive or SSD that the test cannot use, choose one large file already on the drive for a copy comparison.
Close other transfers and apps that are using the drive. Connect it through the splitter, use the same cable you plan to test with, and run the test or copy the same file. Note the speed and whether the drive pauses or disappears.
Safely eject the drive, then connect it directly to a computer USB port. Repeat the same test or file copy with the same cable and file. Do not unplug the drive while it is being read or written.
Repeat each comparison once or twice. A single result can vary because of background activity, drive cache, or the size and type of files. Compare the pattern, not just one peak number.
If the splitter has other devices attached, test the drive with those devices disconnected. Then reconnect them one at a time to see whether one device or the combined load changes the result.

For a practical file-copy check, use a large file of at least a few gigabytes if you have one. A small document may finish before the drive reaches a steady speed. Keep the original file and destination the same for both connections, and do not use a file containing private information if you do not need to.

What the result means

The drive is consistently slower through the splitter

The splitter, its cable, its power supply, or another attached device is a likely cause. The hub may share its upstream connection across ports, so a fast drive cannot necessarily use its full link speed while other devices are active. If the drive also disconnects through the splitter, power or a loose connection is more likely than a simple speed limit.

The results are similar in both connections

The splitter is probably not the main limit in this test. The drive itself, its cable, the computer's USB port, or the type of files being copied may set the speed. A browser test is only a practical comparison, not a full hardware diagnosis.

The drive disconnects only through the splitter

That points to a connection or power problem. Portable hard drives can draw more power when they start or work hard. A bus-powered splitter, which gets its power from the computer, may not supply enough for every attached device at once.

Speed changes a lot from one run to the next

Check whether another device is transferring data through the splitter, and close apps that are reading or writing to the drive. The drive may also slow after its fast cache fills. If the browser test does not list your drive, use the same file-copy comparison instead of treating the missing result as a fault.

How to fix it

Connect the drive directly. If it is reliable and fast on a computer port, use that connection for large transfers or important backups. This is the simplest way to rule out the splitter.
Try a powered hub. A powered hub has its own power adapter. Check that the adapter is connected and is the one supplied or recommended for the hub. Do not use a damaged power adapter or force a connector that does not fit.
Move other devices to a different port. Put high-traffic devices, such as another external drive or a camera, on a separate computer port rather than on the same hub. A hub can share its connection even when each socket looks like a separate port.
Check the cable and connectors. Try a short, undamaged cable that fits the drive and supports data. If the connection changes when the cable moves, stop using that cable or splitter until you can replace it.
Test while the computer is plugged in. On Windows 11, open Settings › System › Power & battery › Power mode and choose Best performance for the comparison. On a Mac laptop, open System Settings › Battery and turn off Low Power Mode if it is enabled. These settings can affect power use, but they cannot repair a weak hub or cable.
Restart and retest. Eject the drive safely, restart the computer, and compare the direct and splitter connections again. If only the splitter still fails, replace it with a suitable hub rather than repeatedly reconnecting a drive during active transfers.

When the drive may be the problem

If the drive is slow or disconnects when connected directly with a known-good cable, the splitter is not the only suspect. Test the drive on another computer if possible. Repeated pauses, error messages, unusual clicking from a mechanical drive, or files that cannot be read may indicate a drive fault. Stop copying valuable data to it, and back up anything you can still read before running more tests.

If the direct-versus-hub comparison points to the splitter, why external drives slow down through USB hubs explains how shared bandwidth and power can affect transfers.

Why one speed number can mislead

USB speed is not just a label on the hub. The computer port, hub, cable, drive, and other connected devices all affect the connection. The slowest part can limit the whole path, and a hub's advertised maximum does not mean every attached device gets that speed at the same time.

Also, a browser-based test cannot prove that a drive is healthy or identify the exact USB version of every part in the connection. Use it as one comparison for supported flash drives and cards. For an external SSD or hard drive, a repeatable copy test and a direct-port comparison are more useful for deciding whether the splitter is involved.