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Why when I transfer a file through SFTP, it takes longer than FTP?

Asked 2012-01-13T10:41:04.483
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I manually copy a file to a server, and the same one to an SFTP server. The file is 140MB.

FTP: I have a rate arround 11MB/s

SFTP: I have a rate arround 4.5MB/s

I understand the file has to be encrypted before being sent. Is it the only impact on the file transfer? (and actually this is not exactly transfer time, but encryption time).

I am suprised of such results.

performance file ftp sftp transfer
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1 Answer

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Several factors affect speed of SFTP transfer:

  1. Encryption. Though symmetric encryption is fast, it's not that fast to be unnoticed. If you comparing speeds on fast network (100mbit or larger), encryption becomes a break for your process.
  2. Hash calculation and checking.
  3. Buffer copying. SFTP running on top of SSH causes each data block to be copied at least 6 times (3 times on each side) more comparing to plain FTP where data in best cases can be passed to network interface without being copied at all. And block copy takes a bit of time as well.
answered 2012-01-13T14:03:14.157

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