# Performance Improvements

FreeFileSync can be set up to issue multiple file accesses in parallel. This speeds up synchronization times dramatically in cases where single I/O operations have significant latency (e.g. long response times on a slow network connection) or they cannot use the full bandwidth available (e.g. an SFTP server that has a speed limit for each connection).
The number of parallel file operations that FreeFileSync should use can be set up for each device individually in the Comparison Settings dialog. It is evaluated for all folder pairs of a configuration as follows:

- During comparison FreeFileSync groups all folders by their root devices.
  For example, consider a configuration with two folder pairs and parallel file operations set up:

  C:\Source | ↔ | D:\Target
  C:\Source2 | ↔ | E:\Target

  Parallel operations | Device root
  1 | C:\
  2 | D:\
  3 | E:\

  FreeFileSync will put the folders C:\Source and C:\Source2 into the same group and allow only 1 file operation at a time. Folder D:\Target will be traversed using 2 operations, and E:\Target using 3 operations at a time. In total FreeFileSync will be scanning all four folders employing 6 file operations in parallel.
- When synchronizing a folder pair FreeFileSync will use the maximum of the number of parallel operations that the two folders support.
  In the previous example the folder pair C:\Source ↔ D:\Target will be synchronized using 2 parallel operations, and C:\Source2 ↔ E:\target will be using 3.

Note
FreeFileSync implements parallel file operations by opening multiple connections to a device. Some devices like SFTP servers have limits on how many connections they allow and will fail if too many are attempted; see (S)FTP Setup.