External drives · Speed, cables and hardware
Why is my external SSD slower than the speed on the box?
Short answer: Box speeds are best cases. Real copies slow down because of the cable or port, hubs, many small files, the drive's cache filling or warming up, or a slower drive on the other end. Check the connection speed in System Information.
The figure on the box is a best case under ideal conditions. Real copies are slower for several ordinary reasons, and one weak link limits the whole chain.
Common causes:
- Cable or port — a cable or adapter that only supports slower USB, or a hub.
- The Mac's port — the drive may support a faster standard than the port.
- Lots of small files — they copy far slower than one large file.
- Sustained copies — many SSDs slow down after their fast cache fills, or when they get warm.
- The other drive — a copy is only as fast as the slower side.
Check the negotiated speed in System Information — see how to see a drive's connection speed. Storage Studio's speed test reports what you really get rather than the box figure.