Slow downloads using SFTP
Situation:
PC on one coast of USA
Unix (solaris) server on the other coast of the USA, running OpenSSH_5.6p1-hpn13v10
Ping: 80ms
Network connectivity: WAN network speed - 40mbps
Over long distance (WAN) on a tuned system, WinSCP 4.3.1 using SFTP (protocol ssh-2) caps around 690kbytes** on download and upload. Cipher AES or blowfish does not make a significant difference. (Ciphers make a large difference during local performance where CPU is more of an issue.)
We found that switching to Filezilla removed the download cap, reaching up to 4.4MB/s (40mbps - which was near the limit of the line). Upload was capped at 650kbytes, which has since been removed by the Filezilla devs (Fixed as of 3.3.5)
Speed difference:
Filezilla results: Transfer of 600mb file in 3minutes. 4.4MB/s
WinSCP 4.3.1 beta results: Transfer of the same 600mb file in 14minutes. 689KiB/s