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I am developing a C# Console Application which downloads files from an SFTP Server with SSH Key Pair Authentication.

I am using the Chilkat API.

The files I am attempting to download are very large, between 8GB-13GB.

Currently the max download speed I can get using my app is around 570 KB/s

If I try to download the same file using FileZilla I get downloads speeds of 2.6 MB/s

Running from the same computer on the same network.

Is there anyway to match the download speeds of FileZilla with a console app?

Isaac Vallee
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  • Welcome to SO. You can update your own question by editing it. You can vote for questions (upvote or downvote) and if you get the answer that satisfies your needs and answers your question, you can mark it as an answer – Eugene Mayevski 'Callback Jul 12 '11 at 06:53

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I know this is super old but no one has explicitly answered it yet. Chilkat recommends increasing the SoRcvBuf and SoSndBuf sizes if you are having network performance. I was having the exact same issues as you and this fixed my problem.

From ChilKat documentation:

public int SoSndBuf {get; set; }

Sets the send buffer size socket option. Normally, this property should be left unchanged. The default value is 0, which indicates that the send buffer size socket option should not be explicitly set (i.e. the system default value, which may vary from system to system, should be used).

This property can be changed if upload performance seems slow. It is recommended to be a multiple of 4096. To see the current system's default send buffer size, examine the LastErrorText property after calling any method that establishes a connection. It should be reported under the heading "SO_SNDBUF". To boost performance, try setting it equal to 2, 3, or 4 times the default value.

Community
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zjacobs
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You probably need a larger TCP maximum window size: http://msdn.microsoft.com/en-us/library/ms819736.aspx

The .NET function to control it is Socket.SetSocketOption(SocketOptionName.ReceiveBuffer)

Ben Voigt
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I had this problem before when I set the byffer size too small.

For realistic results, buffer size should vary according to filesize. You don't want small buffers for big files (your case, where bottleneck is your app managing the buffer, not the connection speed).

You also don't want big buffers for smaller files, so that you won't follow the progress.

Adriano Carneiro
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SFTP is secure, that's why it's downloading at a slower rate. If you want similar speeds, you should download using FTP or attempt to modify the server settings to allow for non-limiting speeds.

Nahydrin
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  • Oh... then it's the Chilkat API. Somewhere in there it's slowing down the download speed. When downloading you set a predefined array of bytes (usually 4kb in size) to continuously read and write the file, FileZilla may be using a larger array. – Nahydrin Jul 08 '11 at 23:26
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There are several factors that influence SFTP speed. SSH buffer size, SFTP buffer size, pipeline length are among those factors (encryption algorithm is another one). One more factor is a language. Optimized C++ code will always be faster than C# code. So while you can achieve comparable speeds with FileZilla, you are unlikely to match them.

Also did you check alternative SFTP components (there are plenty of them on the market)?

Eugene Mayevski 'Callback
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  • It's definately something with the Chilkat API. I tried the Rebex SFTP API and downloads were the same speed. Then I saw Rebex has an option called UseLargeBuffers (which increases buffer size and TCP Window size), and after enabling downloads exceeded 2.8MB/s. Unfortunately I only have a license for Chilkat, so I emailed them and let them know about increasing buffer size and TCP Window size. They are looking into it. – Isaac Vallee Jul 12 '11 at 19:12