I have improved WinSCP by increasing its receive buffer. What should improve download speed, without a need to tweek Windows registry. Anyone willing to test?
Issue 1273 – Increase size of connection receiving buffer

In Windows 7, 64 bit, MAKE SURE you are selecting the 64 bit version of dword when adding the values. (32 bit won't work, 64 bit works a charm!)

Thank you for this tip, it took my transfer speeds from 40 KB/s to 300+ KB/s

LIFE SAVER TIP! :)

@nonotford: I do not see any mention of reusing the connection for multiple transfers.

Some clients support this capability. I'm not sure that is is part of the FTP protocol itself, but a workaround where the client perhaps opens several control connections – not sure.
Here's a client that supports it – <invalid hyperlink removed by admin>

@nonotford: Does FTP protocol allow that? I do not think so.

It seems that WinSCP, when configured for FTP over TLS (FTPS), opens a separate TCP connection for each file transfer. For copying folders with many files and sub-directories, this is extremely inefficient. Each new TCP connection needs to get the certificate before the transfer. Shouldn't there be a way of re-using existing open connections? And re-using multiple concurrent connections at that?

BTW - setting the "Maximal number of transfers at the same time" to 9 (max) does not seem to address this issue.

This is very cool information.

Now the discussion changes from "Why am I slow?" to "How fast can I go?"

I poked around a little and found this link
https://www.speedguide.net/articles/windows-2kxp-registry-tweaks-157

They have some recommendations for what value should be in there.

A friend of mine recommended this software:
https://www.avg.com/en-ww/avg-pctuneup

There is a free trial version.

Oh, and as always – when tweaking the registry, back it up and update your will.

@martin: No Problem. We also found this does speed up SFTP uploads on Vista, Windows 7, and Server 2003 "clients".

@trevz: Thanks for sharing this!

We experienced similar SFTP transfer speed caps from some of our Windows XP desktops to one of our vendors SFTP servers. The weird thing was that some Windows desktops seemed to be capped at 100KB/s for upload (averaged more like 80KB/s), and other desktops on the same LAN would get around 400KB/s uploads. After ruling out NIC hardware or drivers, we accidentally made of of the "capped" desktops upload to the SFTP site at 400KB/s. We discovered that SFTP uploads speeds increased after installing the Citrix XenApp client. After comparing the registry before and after the install, we discovered that the Citrix client modifies TCPIP and ADF parameters in the registry.

After the below reg entries were added to a XP client which was experiencing slow upload speeds, (reboot system after reg change), the client was able to upload at over 400KB/s

DefaultSendWindow and TcpWindowSize value are added

This issue has been added to tracker:
Issue 164 – Slow file transfers

Can you try PSCP/PSFTP for comparison? WinSCP SSH code is based on PuTTY package. I cannot make WinSCP faster than they are.

To add to this, I can do 3 or more parallel transfers and each one caps at 100KBps showing that not only can my computer and the server keep up with faster transfers, but that WinSCP can do multiple ones in parallel beyond the cap of 100KBps (or a fractional percentage of the total speed available).

To me, this just makes it seem like there is some sort of arbitrary cap being put in place by WinSCP for each individual transfer.

I've also tried every encryption algorithm, multiple machines, SFTP vs SCP, SSH1 vs SSH2, etc. Everything I do on multiple machines seems to be capped at around 100KBps upload speed. One machine is a Core 2 Duo at 2.0GHz with a 7200rpm disk and while WinSCP is uploading, the CPU idles at around 10% or so, no where near it's processing limit. This happens on both Windows Vista SP1 and Windows XP SP2. We've tested our routers and firewalls by using a slower Linux machine that easily uploads at our full upload bandwidth (7.5Mbps).

@martin: I tried many things without gaining more speed.
Have you tested WinSCP and normal console scp under Linux on the same hardware?

aruzsi wrote:

So I know scp eats CPU power but why not under Linux?

Maybe different encryption algorithm? It can also be fault of WinSCP. Have you tried psftp/pscp?

OK.

I've read the FAQ.
I don't know why there is so much difference on the same hardware. Of course I tried many options and 1Mbps was the best.
I tell you again: everything is the same except OS (and client). So I know scp eats CPU power but why not under Linux?

TIA,

Please read FAQ.

Hi,

Can you tell me why so slow WinSCP?
On a fast Ethernet network WinSCP reaches 1Mbps.
On the same hardware normal Linux scp is 7Mbps.

TIA, Ruzsi