Slow downloads using SFTP

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aliengerm1
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Slow downloads using SFTP

This is a repeat and summary of a related post.

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

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aliengerm1
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I can only make an educated guess and say that I think the problem lies with a too small socket receive buffer.

More research:
I found another tool that has adjustable send/receive buffers. The default it negotiated was 1024kbytes, which was still slow. The ideal for this particular line seems to be 2048kbytes. My guess is that WinSCP has 512 send/receive buffers. Those should at minimum be upped to 1024 in general, and consider makeing that a user adjustable parameter since its useful particularly on large and long lines, aka WAN.

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martin
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Re: Slow downloads using SFTP

Thanks for your investigation. I'll check it.
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Martin Prikryl

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aliengerm1
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Thank YOU.

Update: I had a bit of software that had a default of 128kbytes, which autotuned to 1024kbytes for socket receive buffer. I then set default to 2048, then it autotuned to 4096. Autotuned = tcp sliding window adjustment, in the socket receive buffer. That's for download only, that particular bit of software performed poorly when it came to upload, so no good numbers.

I hate to put you on the spot but do you consider this a priority item or a low level item?

Thanks again.

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martin
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aliengerm1 wrote:

I hate to put you on the spot but do you consider this a priority item or a low level item?
Rather of priority. Which means I'll take a look at it in a week or two.
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Martin Prikryl

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aliengerm1
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winscp 4.3.2

I just tested the latest version, WinSCP 4.3.2.

(600mb test file)

California PC download from East Coast OpenSSH server using WinSCP 4.3.2 ~15minutes, high speed around KiB/s

California PC upload to East Coast OpenSSH using WinSCP 4.3.2 ~16minutes, high speed around 640 KiB/s


Sorry :(

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martin
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Re: winscp 4.3.2

By coincidence I have done some tests yesterday too. But I had no luck so far.

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ErikSorensen
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Re: winscp 4.3.2

Hi - came across this thread while googling this issue. Just to add my .02 -- I have 3.8.2 installed side by side with 4.3.2 on the same machine - 3.8.2 gets 4300 KB/s while 4.3.2 gets 30 B/s while trying to sftp upload to the same server.

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bmorgan
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slow speeds with 4.3.2

i too am seeing very slow speeds when uploading files from my winxp pc to a redhat 5 linux machine (also slow to aix and solaris machines) (14mb in 24 minutes)

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martin
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Re: winscp 4.3.2

ErikSorensen wrote:

Hi - came across this thread while googling this issue. Just to add my .02 -- I have 3.8.2 installed side by side with 4.3.2 on the same machine - 3.8.2 gets 4300 KB/s while 4.3.2 gets 30 B/s while trying to sftp upload to the same server.
Can you try 4.2.9 for comparison?
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Guest

4.28 was now also slow... checked my speed setting on the NIC and it was set to "Auto" - changed this to 100 Full and am now working normally again (3mb sec)

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andilao
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Today tested on a new Server 2008 R2, 2x Xeon E5620:
        DSL 10MBit/s   LAN 1GBits/s
WinSCP      208 KiB/s    2650 KiB/s
Tunnelier   210 kB/s     --
FileZilla   675 KB/s     13 MB/s !!    

FTP over LAN 1GBits/s for comparison:
     
WinSCP      ~60 MB/s 
FileZilla   ~75 MB/s    

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Tranton
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I get just the same problem when I try and login to my school's server to transfer something,
Error: ssh_init: Host does not exist
Error: Could not connect to server

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Guest

I did little test here:

Server: CentOS 5.6 x64 + SSH 5.8p1-hpn13v11 / vsftpd 2.0.5
Network: GigaLan
Client: Windows 7.1 x64 + WinSCP 5.0beta / FileZilla 3.5.1
File: 524 MB

WinSCP (SFTP-3 arcfour) download 22.5 MB/s
WinSCP (SCP arcfour) download 16 MB/s
WinSCP (FTP) download 105 MB/s

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Guest

Continue to the previous post.

WinScp (SFTP-3 AES-256) download 10.5 MB/s

FileZilla (SFTP AES-256) download 12.6 MB/s
FileZilla (FTP) download 105 MB/s

Tunnelier 4.4

Tunnelier (SFTP AES-256) download 15 MB/s
Tunnelier (SFTP arcfour) download 24 M/s

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