Performance

All credits for detailed performance testing goes to Michael Stiemke.

What are the typical file transfer speeds I can expect?

Test results

The following table shows the typical transfer speeds on various different Client CPUs, using both sync and async FTP clients.

FluentFTP Class	Application	Download speed	Upload speed	Client CPU
FtpClient	WinForms	111 MB/sec	80 MB/sec	Intel Core i9-13900K
AsyncFtpClient	WinForms	111 MB/sec	80 MB/sec	Intel Core i9-13900K
FtpClient	Console	111 MB/sec	80 MB/sec	Intel Core i9-13900K
AsyncFtpClient	Console	60 MB/sec	80 MB/sec	Intel Core i9-13900K
FtpClient	WinForms	111 MB/sec	80 MB/sec	Intel Core i7-6700HQ
AsyncFtpClient	WinForms	80 MB/sec	80 MB/sec	Intel Core i7-6700HQ
FtpClient	Console	111 MB/sec	80 MB/sec	Intel Core i7-6700HQ
AsyncFtpClient	Console	60 MB/sec	80 MB/sec	Intel Core i7-6700HQ

Test conditions

These are the test conditions that were used to measure the file transfer speed.

• Network
  • Network transfer rate: 1Gb/s
• File
  • File size: 1GB
  • File contents: Random bytes
• Server
  • Server CPU: Core I9-10900K
  • Server Hard Disk: 1500MB/s SSD
  • Server Operating System: Debian 11
  • Server FTP Software: ProFTPd
• Client
  • Client CPU: Mentioned in the table above
  • Client Operating System: Windows 10
  • Client Hard Disk: 1500MB/s SSD
  • .NET Build type: Release build
  • .NET version: .NET 6
  • .NET application: WinForms or Console Application
  • Library version: FluentFTP V50.0.1
  • Stream type: SslStream, in-built in FluentFTP (Performance of FluentFTP.GnuTLS was equivalent in all cases)

What aspects influence FTP file transfer speed?

1. Network speed/latency

While the influence of network transfer speed is a major factor in the performance of large data transfers, the transfer of very many small files will profit also from overall network latency and round-trip times, as the command-response sequences on the control connection become a bottleneck.

2. Server CPU / IO performance

The server must of course be able to supply or ingest data fast enough fully utilize the available network resources.

3. Client CPU / IO performance

The client must also not be hampered by a slow or busy CPU whilst the IO performance will seriously slow down transfers.

4. .NET Version

The newer the version of .NET that you target, the better your results will be. The differences in CPU usage between older .NET Framework versions and .NET 6, for example, can be very significant, especially when using async methods. Your file transfer can easily become CPU bound and thus your transfer times will scale to your CPU and not your network.

Is FTP a slow file transfer protocol?

No, FTP(S) was designed to have virtually no protocol overhead on the data transfer itself. No overhead, that is, other than that imposed by Ethernet, as well as IP and TCP. You can't get much better than that.

What is the theoretical maximum file transfer speed?

Theoretical maximum transfer rate on a 1Gb/s ethernet connection, taking all ethernet frame headers into account would be 118MB/sec (even 123MB/s using jumbo frames = 99% of 1Gb/s).

Now take into account IP / TCP headers, which can be minimised by avoiding fragmentation, using jumbo packets, avoiding resends, delaying ACKs and other measures. This can be estimated at about 2.8% of the available bandwidth, so we arrive at a speed of about 114MB/sec.