Why is my external drive so slow?
Usually the port, the cable or the kind of files being copied — not the drive. How to tell which, in the order that finds it fastest.
- Difficulty
- beginner
- Time
- 30 min
- Read
- 4 min
Short answer
Check four things in order. The port: a drive in a slow USB port runs at a fraction of its speed, and older ports look identical to newer ones. The cable: a charging cable will carry data at the slowest possible rate or not at all. The file mix: thousands of small files copy far slower than one large file of the same total size, on any drive. The drive itself: a mechanical drive that is nearly full, fragmented or failing will crawl, and so will a cheap USB stick.
Copy speed is set by the slowest link, and there are five links. Working along them in order takes a few minutes and almost always finds it.
Step by step
- Check which port it is in.Ports of different generations often look the same. Blue plastic inside a rectangular port generally indicates a faster generation; black often indicates the oldest. A modern drive in an old port is capped at a small fraction of its capability. Try each port on the machine and compare.
- Check the cable.Many cables supplied with phones and accessories carry power and only the slowest data, or no data at all. Use the cable that came with the drive, and if you must substitute, use one explicitly rated for the drive's standard. This is the most common single cause.
- Avoid unpowered hubs for drives.A hub shares one connection between everything on it, and an unpowered hub may not supply enough current for a mechanical drive, which produces both slowness and dropouts. Connect a drive directly, or use a powered hub.
- Look at what you are copying.One 10 GB video copies at close to the drive's rated speed. Ten thousand small files totalling 10 GB copy several times slower, because each file has fixed overhead. This is normal and not a fault. For lots of small files, compress into one archive first and copy that.
- Check how full the drive is.A mechanical drive slows markedly when nearly full, both because the outer, faster part of the platter is used up and because free space is scattered. Above about ninety per cent, expect a noticeable drop.
- Check the file system.A drive formatted as FAT32 or exFAT for compatibility handles large numbers of small files less efficiently than NTFS or APFS, and exFAT in particular can be slow for that pattern. If the drive only ever meets one platform, format it natively.
- Rule out background work.Antivirus scanning every file as it is written, an indexer cataloguing the new drive, or a backup running to the same drive will all halve the apparent speed. Check what is running before blaming the hardware.
- Then suspect the drive.If it is slow on every port, every cable and every machine, look at its health data. A mechanical drive retrying bad sectors produces exactly this symptom, with the speed dropping to almost nothing in patches and then recovering.
If it doesn't work
Copy starts fast then collapses to a crawl
Cause: The write cache filled and the drive is now writing at its true sustained speed — normal on cheap SSDs and USB sticks — Fix: Nothing to fix; it is the drive's real speed. If it matters, buy a drive with a stated sustained write speed rather than only a peak figure.
Drive is slow only on one computer
Cause: Old ports, a driver or power-saving setting on that machine — Fix: Compare ports, try the same cable and drive on another machine to confirm, and check whether the machine has any faster ports on a different side or on a dock.
Speed varies wildly between transfers
Cause: Mixed file sizes, background scanning, or an intermittent cable — Fix: Test with one large file to get a clean measurement, then reintroduce variables one at a time.
Estimated time remaining is wildly inaccurate
Cause: The estimate is extrapolated from recent throughput and file mix — Fix: Ignore it in the first minute and for mixed content. Judge by whether files are still appearing at the destination.
Drive spins up slowly every time it is used
Cause: Power saving is parking or spinning down the drive after a short idle period — Fix: Adjust the sleep timeout for external drives in the system's power settings if the delay is annoying. It is not a fault.
Questions people ask
Should I buy an external SSD instead?
For anything you work from directly, yes — the difference is large and immediately felt. For a backup drive that runs unattended, mechanical is far better value per terabyte and the speed matters less.
Why is my drive slower than the number on the box?
Those figures are peak sequential speeds under ideal conditions, quoted in bits rather than bytes for interfaces, and never reached in normal mixed use. Half the headline figure on a large single file is a good real-world result.
Does the enclosure matter?
Yes. A fast drive in a cheap enclosure with an old bridge chip runs at the enclosure's speed. If you are reusing a drive in a caddy, buy the caddy on its stated standard, not its price.