Why is SCP so Slow and How to Make it Faster?

SCP (Secure Copy Protocol) is a popular file transfer protocol used for the secure copying of files between hosts. At times, the speed of transfer can be sluggish, particularly when transferring large files or when the transfer is over long distances.

This article aims to explore all the reasons that make the SCP slow and how a user can make it faster by discussing the below content.

  • Factors Affecting SCP Speed
  • Methods to Improve SCP Speed

Factors Affecting SCP Speed

SCP is a file transfer protocol commonly used on Unix-based systems and provides a simple and secure way to transfer files. However, SCP has some limitations that can make it slow, which are mentioned below:

Factor 1: Network latency

Network latency is one of the major factors affecting SCP speed. Latency refers to the duration taken by data packets to travel from one point to another. Higher latency indicates an extended transit time to reach their intended destination. SCP requires an acknowledgment from the receiving host for each packet, and high latency can lead to frequent timeouts and retransmissions, slowing down the transfer speed.

Factor 2: Bandwidth Limitations

SCP uses the TCP protocol for data transfer, which has its limitations. TCP is designed to ensure reliable data transfer, which means it can slow down the transfer speed if there are packet losses or errors.

Factor 3: Encryption Overhead

SCP uses encryption for secure data transfer, which adds overhead to the transfer process. Encryption requires additional processing power and can slow the transfer speed, especially on older or less powerful hardware.

Methods to Improve SCP Speed

Now after looking at the major factors, let’s look at some tips to make it faster:

Method 1: Use a Faster Cipher

SCP supports various encryption algorithms, each with different performance characteristics. The default cipher utilized is AES-128, which balances safeguarding and efficiency. However, if speed is a priority, using a faster cipher such as RC4 or Blowfish can significantly improve transfer speeds.

Method 2: Use Compression

SCP supports compression, which can reduce the amount of data that needs to be transferred, which can be especially effective for transferring large files or over slow networks. The compression level can be adjusted to balance the compression ratio with the processing overhead.

Method 3: Limit Bandwidth Usage

Limiting the bandwidth used by SCP can improve transfer speeds, especially when other network traffic is competing for bandwidth. SCP supports bandwidth limiting, which can restrict the transfer speed and prevent SCP from saturating the network.

Method 4: Use a Parallel Transfer

SCP supports parallel transfer, which allows multiple files to be transferred simultaneously. This can significantly improve transfer speeds, especially when transferring multiple large files.

Method 5: Use a dedicated SCP Accelerator

There are several dedicated SCP accelerators available that can significantly improve transfer speeds. These accelerators use advanced techniques such as compression, caching, and parallel transfer to speed up SCP transfers. Some popular SCP accelerators include Aspera, FileCatalyst, and Tervela.


SCP can be a slow file transfer protocol, but you can use several tips and tricks to make it faster. From using a different protocol to compressing files before transferring, these tips can help you transfer files more quickly and efficiently. Remember that the specific approach that works best for you will depend on your situation.