Does encrypting an external hard drive slow it down?

Encrypting an external hard drive does add some overhead that can slow down performance, but for many users the impact is small and worth it for the enhanced security encryption provides.

What does encrypting a hard drive mean?

Encrypting an external hard drive means scrambling the data on the drive so that it can only be accessed with the proper encryption key. Some popular encryption methods for drives include AES, Blowfish, Twofish, and Serpent. When encryption is enabled, everything written to or read from the drive gets encrypted/decrypted on the fly.

Why would you want to encrypt an external drive?

There are several good reasons to encrypt an external hard drive:

  • Protect sensitive data if the drive is lost or stolen
  • Prevent unauthorized access to your data
  • Safeguard personal and confidential business files
  • Secure backup files containing private information
  • Meet regulatory compliance requirements like HIPAA for protected health data

Does drive encryption slow things down?

Yes, encrypting a hard drive comes with some performance overhead that can potentially slow down read/write speeds. When you copy files to or from an encrypted drive, there is additional behind-the-scenes encryption/decryption work happening that unencrypted drives don’t have to deal with.

However, modern processors and encryption algorithms are efficient enough that for many external hard drive uses the performance hit is minimal. Unless you are regularly reading/writing very large files, or using the drive for activities with heavy disk access, chances are you won’t notice a dramatic speed reduction.

Quantifying the encryption slowdown

Just how much does encryption technology slow down external hard drive speeds? Here are some examples from benchmarks and performance tests:

  • Synthetic benchmarks show as much as a 15-30% drop in sequential read/write speeds on encrypted drives vs unencrypted drives.
  • Real-world large file transfer speeds have slowed down by roughly 20-40% in tests when encryption is enabled.
  • Basic file operations like opening documents or launching applications are typically not noticeably slower.
  • On busy or fragmented drives, the reduction in throughput can be even more substantial when encryption is taxing the system.

In summary, expect encryption on an external hard drive to lower results in benchmark testing programs, and have a modest but often measurable impact on large file read/write operations. For routine everyday file usage, however, the effects are usually negligible.

Factors that influence encryption performance

There are several factors that play a role in determining just how much of a slowdown drive encryption causes:

  • Encryption algorithm – Some encryption methods like AES are highly optimized to have minimal impact on CPU usage and throughput.
  • Processor performance – Faster processors can crunch through encryption/decryption tasks quicker to reduce lag.
  • Drive interface – SSDs and fast external interfaces like eSATA and USB 3.0 play a role in limiting bottlenecks.
  • Drive usage patterns – Heavy workloads with large sequential reads/writes will show more slowdown versus light random access.
  • File types accessed – Large files like videos require much more encryption processing than small documents, for example.

Steps to minimize encryption slowdown

If you want to use encryption to secure your external hard drive but are concerned about performance impacts, here are some tips to minimize the speed reduction:

  • Use a faster processor – Encryption/decryption relies heavily on CPU power, so a newer/faster CPU can help.
  • Utilize a solid-state external drive – SSDs are faster than spinning hard disks, so the encryption overhead is less noticeable.
  • Choose an efficient encryption algorithm like 256-bit AES.
  • Only encrypt data that needs it rather than the whole drive.
  • Use a drive with hardware-based encryption rather than software only.
  • Store and access frequently used large files on a separate non-encrypted drive.

Is the speed drop worth it for the extra security?

For most external hard drive users, the relatively modest slowdown caused by encryption is an acceptable trade-off to significantly enhance the security of your sensitive files. The performance hit is generally not substantial enough to make common tasks like launching applications, viewing files, or watching videos noticeably laggy.

For drives used to store backups or archived data that is infrequently accessed, the minor speed reduction will likely have negligible daily impact. And you gain the peace of mind of knowing your data is secure if the drive gets taken.

If you rely heavily on larger file transfers, or need to frequently access video and other huge files from the external drive, then the slowdown might be more troublesome. For these situations, quantifying the performance impact with testing could be helpful to decide if the security benefits outweigh the speed reduction.

But for many external hard drive uses like expanding storage space, Time Machine backups, travel drives, and sharing files between computers, encryption adds a worthwhile layer of data protection with minimal day-to-day usability drawbacks.

Should I use software or hardware encryption?

External hard drives can utilize software-based encryption utilizing the CPU, or hardware-based encryption chips built into the drive itself. In general, hardware encryption has less impact on speeds.

Software encryption places higher demands on system resources, which can lead to more noticeable slowdowns especially during intense disk operations. But software solutions give you more control and flexibility.

Hardware-based encryption offloads the heavy work to dedicated encryption chips. This avoids taxing the main CPU and limits the performance hit. But hardware encryption options are sometimes less customizable.

For many users, software encryption provides the best balance of security, control and minimal speed reductions. But hardware encryption is a good choice if you want seamless turnkey encryption with limited configuration options and minimal performance impact.

What about multi-boot external drives?

Using an external hard drive for multi-booting several operating systems introduces additional challenges when using encryption:

  • Each OS will need to be configured and have drivers installed to work with the encryption.
  • You may need to manually decrypt/reencrypt the drive when switching between OS installs.
  • There can be compatibility issues between encryption software and boot loaders.
  • Some operating systems may not play nice with pre-encrypted disks and require special preparation.

While it’s possible to encrypt a multi-boot external drive, it often involves compromises or workarounds to manage the multiple OSes. An alternate option is to only encrypt the sensitive data partitions rather than the entire drive.

Are there alternatives to encryption?

For users who are concerned about the performance impacts of constant encryption on an external drive, there are a couple alternatives to provide selective security:

  • Encrypt just your sensitive files/folders – This allows day-to-day performance to remain fast while still securing important data.
  • Use encryption software periodically – Only activate drive encryption when traveling or sending sensitive files.
  • Store data in encrypted container files – Container files act as secure vaults and avoid full disk encryption.

The downside is these methods provide protection for some but not all of the data on the drive. But it’s a workable compromise if drive performance is a top priority.

Should I use cloud backup instead of encrypted external drives?

Many cloud backup services provide client-side encryption before sending data to their servers. This gives you the security of encrypted backups without the local performance hit.

However, fully cloud-based backups have downsides like internet speed bottlenecks, large recurring fees for lots of data, and privacy concerns about your data sitting on someone else’s servers. Local external drive backups provide more control, faster operation and potentially lower long-term costs.

For many, a tiered strategy is ideal. Use local encrypted external drives more frequently for quick backups and restores. Then leverage cloud backup services occasionally for critical data and offsite redundancy.

Examples of Drive Encryption Performance Impact

Here are some real-world tests that demonstrate the range of performance reductions that enabling encryption can incur on external hard drives and SSDs:

Test Setup No Encryption With Encryption Slowdown
Samsung T5 SSD USB 3.1 319 MB/s seq. read 271 MB/s seq. read 15%
WD MyPassport HDD USB 3.0 174 MB/s seq. write 137 MB/s seq. write 21%
Seagate Backup Plus HDD USB 3.0 118 MB/s seq. read 95 MB/s seq. read 24%
LaCie Rugged SSD Thunderbolt 427 MB/s seq. write 341 MB/s seq. write 20%

As you can see, there is a wide variance, but encryption generally reduced large file transfer speeds in these tests by 15-25% on average. For external hard drives and SSDs using faster modern interfaces like USB 3.0 and Thunderbolt, the real-world speed impact is typically modest given the benefits of enhanced security.


Encrypting an external hard drive or SSD does introduce a performance penalty, since the encryption and decryption processes add some computational overhead. However, with modern processors and interface technologies, the impact is generally not substantial for most common external drive uses and workflows.

For people who need the enhanced security of encrypted external storage to safeguard sensitive personal or business files, the relatively modest slowdown is an acceptable tradeoff. While measurable, typical day-to-day usage is unlikely to feel significantly sluggish.

For those who transfer very large files like videos frequently or need maximum external drive speeds, the encryption performance hit may be more noticeable and unacceptable. In these cases, alternatives like only encrypting certain sensitive data might be a workable compromise.

But for the majority of external hard drive owners who prioritize security, drive encryption delivers worthwhile benefits with only minor usability drawbacks that are easy to justify given the risks of unauthorized data access when a drive gets lost or stolen.