Slow download network speed over plink

[vovcacik]

Hi,
I've noticed that plink download speed is considerably lower than the speed of other implementations. It only affects plink and only the download speeds; upload is as fast as others. I tried vanilla plink and PuTTYTray plink.

Server side setup

• server is Debian running on Amazon's EC2
• we just need some test file; in this case binfile of size 100 MiB in home dir

cd
dd if=/dev/zero of=binfile bs=$((2**20)) count=100

ls -la binfile
-rw-r--r-- 1 admin admin 104857600 Aug 12 11:10 binfile

Client side setup

• client is Windows 10
• I've got installed:
  • Win32-OpenSSH
  • vanilla plink (direct link ftp://ftp.chiark.greenend.org.uk/users/sgtatham/putty-0.66/)
  • puttytray plink
  • unison version 2.40.69 (synchronization tool, similar to rsync)

set path=C:\Program Files\OpenSSH;C:\putty;%PATH%

• and the benchmark:

# Win32-OpenSSH performance

scp admin@nano.ovcacik.org:binfile binfile
echo 12.66s

ssh admin@nano.ovcacik.org cat binfile > binfile
echo 12.74s

unison nano
echo 12.41s



# PuTTY, PuTTYTray performance

pscp -scp admin@nano.ovcacik.org:binfile binfile
echo 12.91s

pscp -sftp admin@nano.ovcacik.org:binfile binfile
echo 12.85s

plink -V
plink: Release 0.66
plink admin@nano.ovcacik.org cat binfile > binfile
echo 74.00s

plink -V
plink: PuTTYTray p0.66-t028
plink admin@nano.ovcacik.org cat binfile > binfile
echo 73.18s

plink -V
plink: PuTTYTray p0.67-t029
plink admin@nano.ovcacik.org cat binfile > binfile
echo 75.60s

unison nano
echo 107.64s

You can see that plink is about 5x slower. I have included unison in the benchmark, as thats the real world use case here, but even the cat binfile over plink demonstrate the problem well.

There is also very nice question on serverfault.com Copying over SSH via Putty tools is slower than via WinSCP.

I know this may not be the best place to ask this, but I wanted to bring this to your attention, because you may have better insight what could be wrong, or you may have noticed some build flags that could help to fix this.

[T-O-W]

This might not be the same issue, but I observed that all tools based on PuTTYs file transfer implementation (WinSCP, FileZilla, PuTTY tools) have a considerably bad network performance. In a gigabit network, I can transfer files with only about 15 MB/s. First, I thought this was an issue with ciphers, but other tools (Bitvise SSH, Windows 10's Linux subsystem, a native Linux, ...) do a much better job (around 75 MB/s in my case) using the same ciphers.

I don't know what is wrong there, but it seems that PuTTY developers did a very bad job for file transfers. Still, I perfer PuTTY over Bitvise SSH for daily work, because it is more convenient. For big file transfers, I use Bitvise SSH.