Using an external hard drive can sometimes lead to slower performance on your computer. There are a few factors that contribute to this potential slowdown when adding an external drive.
Disk speed
One of the biggest factors is the transfer speed of the external drive. Most external hard drives connect via USB, which has lower maximum transfer speeds than internal SATA connections. USB 2.0 has a maximum speed of 60 MB/s, while USB 3.0 is faster at 625 MB/s. In contrast, SATA 3 has maximum speeds up to 1969 MB/s.
So any data transfers between your computer and the external drive will be bottlenecked by the USB speed. This includes reading/writing files on the external drive, as well as running programs or games from the external drive. The slower connection can cause lags and delays.
Drive format
The file format of the external drive also impacts performance. By default, most external drives are formatted with the FAT32 file system. This is compatible with both Windows and Mac OS, but has limitations on file sizes and does not offer the fastest performance.
Formatting the drive with a native file system like NTFS on Windows or HFS+ on Mac will allow for faster data transfers. However, doing so may limit the drive’s compatibility with other operating systems.
Drive cache
Another factor is the cache built into the external drive. Most drives have 8-64MB of cache memory to enable faster writes and reads. A larger cache means the drive can temporarily store more data for faster access.
An external drive with lower cache may see slower transfer speeds, resulting in lags when reading or writing files.
Drive RPM
If using a traditional hard disk drive (HDD), the drive RPM impacts performance. Most external HDDs run at 5400 RPM, while internal desktop HDDs are typically 7200 RPM or higher.
The slower rotational speed of 5400 RPM translates to slower read/write times. So external HDDs may cause lags compared to your faster internal drive.
Port throughput
The throughput capabilities of the USB port on your computer also plays a role. Some computers may have USB 2.0, USB 3.0, or USB 3.1 ports. The versions have differing maximum throughputs:
| USB version | Maximum throughput |
| USB 2.0 | 60 MB/s |
| USB 3.0 | 625 MB/s |
| USB 3.1 Gen 1 | 625 MB/s |
| USB 3.1 Gen 2 | 10 Gb/s |
If your computer only has USB 2.0 ports, you may experience bottlenecks when transferring data over USB 3.0 or 3.1. Using a higher throughput USB port can improve performance.
Drive use while operating
Using files and programs on the external drive while the computer is running can also slow things down. The USB bandwidth is shared between active tasks and background processes.
So using bandwidth intensive apps like video editors or games on the external drive while moving files in the background can create lag. Try to avoid using the external drive for active tasks during file transfers.
Insufficient power
Some external drives with higher power requirements may function slower if the USB port cannot provide enough power. This constraint can force the drive to throttle transfer speeds to compensate.
Connecting the drive to a powered USB hub or using an external power adapter can improve performance in this scenario.
Drive fragmentation
Like internal drives, excessive fragmentation on the external drive can reduce performance. Fragmented data takes longer to access since it is scattered across the disk.
Periodically defragmenting the external drive using built-in utilities can help restore speeds.
Older external drives
As external drives age, the internals may deteriorate in performance. Factors like disk errors, bad sectors, and decaying read/write heads can slow down data access.
Upgrading to a newer external drive may see a noticeable boost over older models.
File system overhead
The file system used on the drive also requires disk resources to organize and track data. More complex file systems like NTFS have higher overhead compared to FAT32.
This overhead accounts for a small amount of disk activity that may impact performance. But the benefits of NTFS generally outweigh this cost.
Slow computer processor
A slow computer processor can make any drive access seem slower. Data transfers involve both the drive and the computer itself. A slow processor can become a bottleneck.
Upgrading your computer’s CPU may help improve overall system performance including external drive speeds.
Excessive drive wear
After considerable use, the wear and tear on an external drive motor can degrade performance over time. Symptoms include noisy operation and slower data reads/writes.
This decline is remedied by replacing the external drive.
Too many plugged in USB devices
Having many USB devices connected can tax the bus bandwidth available from your computer. The external drive competes for throughput.
Try plugging the drive into a USB port on a less crowded bus or hub. Also disable any unnecessary USB devices to free up bandwidth.
Poor cable connection
Loose or faulty cables between your computer and external drive can interfere with signal integrity. This could introduce data transfer issues that lower performance.
Inspect cables to ensure snug connections. Swap cables to see if speeds improve.
Using a non-USB 3.0 drive
On computers with USB 3.0 or 3.1 ports, using an older external drive with only USB 2.0 connectivity can bottleneck data speeds. The drive’s interface limits you to slower USB 2.0 transfer rates.
Upgrading to a drive with native USB 3.0 or USB 3.1 connectivity will provide faster transfer speeds.
Drive response time
External HDDs typically have slower response times than internal SSDs and HDDs. Because the drive motors are engineered for portability and travel, they sacrifice a bit of speed.
An internal drive with faster response times would not cause as much lag.
Sharing bandwidth with other devices
If you are sharing the external drive over a network with other users, bandwidth bottlenecks may occur. Network speeds are generally slower than direct USB or Thunderbolt connections.
Ensure your network is sufficient speed for the users accessing the shared drive. Or consider giving each user their own external drive.
Using a low quality cable
Lower quality cables can sometimes impede external drive speeds and cause transfer issues. Inferior cables may get lower voltage/amperage, increasing risk of errors.
Use high quality cables from reputable brands that are properly shielded and constructed.
Tips to improve external drive speeds
If your external drive seems slow, here are tips to potentially improve performance:
- Use USB 3.0/3.1 ports or Thunderbolt ports when available
- Connect the external drive directly to the computer rather than through a hub
- Use shorter cables for reduced interference
- Plug the external drive into a powered USB hub or provide separate power adapter
- Avoid using the drive for active tasks during file transfers
- Defragment the drive if necessary using built-in utilities
- Replace cables to rule out faulty connections
- Test different cables and ports to isolate issues
- Upgrade to a high speed solid state external drive
- Upgrade your computer processor if severely outdated
- Disable unnecessary USB devices to reduce bus congestion
Conclusion
While external hard drives provide a convenient way to expand storage and access data across devices, they can sometimes impact system performance. Several factors contribute to potential slower speeds when using an external drive.
However, with careful setup and configuration, you can optimize external drive speeds. Choose a high speed drive with large cache and native USB 3.0/3.1 support. Connect the drive properly using high quality cables and isolated USB ports. Avoid overusing the drive when performing system intensive tasks. And periodically defragment the drive.
In most cases, taking these steps will minimize any speed reductions when using an external hard drive.