Just a suggestion for folks who need to keep using SCP with an older client host machine: I was maxing out at 100% CPU and getting about 800KiB/s – setting WinSCP to "realtime" in the Ctrl-Alt-Del Task Manager improved that to 1,800KiB/s. This is a P4 2.4GHz processor: no HT, no dual core, old bus.

Not great speed, but way better than before. Of course nothing else is happening on the system, but that's okay – I just need this 4GB transfer to hurry up and finish!

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

@Guest: We have Globalscape, and see that from time to time.

@Guest: Did he/she changed any settings?

We have a user which was sending a 40000 bits a second. Monday this week with the same size file it is sending at 9800 bits a second. This info is from our Globalscape FTP server.

What would cause something like this?

WinSCP does it the same, but with different numbers.
You can alter one of these via options SFTPDownloadQueue and SFTPUploadQueue in the respective session section of WinSCP configuration. The default value is 4, try something larger (like 10).

Some tests on a LAN (server is running OpenSSH 4.5)...

• WinSCP/3.8.2 gets about 2500 KB/s over SCP
  
• WinSCP/3.8.2 gets about 400 KB/s over SFTP
  
• SSH.com Client/3.2.9 gets about 600 KB/s over SFTP
  
• CuteFTPPro/8 gets about 250 KB/s over SFTP
  
• PuTTY PSFTP/0.56 gets about 330 KB/s over SFTP
  
• PuTTY PSFTP/0.58 gets about 100 KB/s over SFTP
  
• PuTTY PSFTP/0.59 gets about 1100 KB/s over SFTP
  

So...

1. The difference between SFTP and SCP was a lot bigger than I had expected.
   
2. Between 0.56 and 0.59 of the PuTTY client, the speed went up by 3x (0.58 was unusually slow; I think it's buggy). Still slower than SCP, but much better than any of the other SFTP tests.
   
3. According to the changelog for version 6722 of sftp.c in the PuTTY CVS, the the 3x speedup is caused "simply by upping the packet sizes and maximum in-flight packet count." The WinSCP code and the PuTTY code are so very different that I can't seem to find anything remotely similar; you are much more familiar with your code than I am; are tweaks like this feasible for WinSCP?
   

@asif: There's no way to set fixed limit of transfer speed.

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Edit 2024: You can set limit at https://winscp.net/eng/docs/ui_transfer_custom

I have the opposite problem... I keep getting disconnected by my cable company when I am using WinSCP. I wonder if it may be because I am exceeding my upstream limit. To test this, I would like to limit my own upload rate. Any way to do this?

Currently I have no idea what I can do to improve speed of transfer in WinSCP.

I love your client and the fact it does so much for free but it seems to need some fixing. I do scp transfer from my server in the Netherlands which uses Debian to my Windows box in the US using SCP. I have a 10 mbit down 1 mbit up line and 100 mbit on the server. Using WinSCP I seem to be limited to 170 KB/sec at best. It seems to get there easy but doesn't want to go past it, even when transferring gigs. If I use scp from my Linux box here, I can almost max out my line. I do that and then transfer using my LAN where security isn't needed via ftp to my Windows box when it comes to really huge filesets. It's just much faster. However, all seems fine when uploading with WinSCP, but then again, my ISP limits me to about 128 KB/sec on the upstream side. I have no processor issues as I have a very powerful CPU, an AMD Athlon FX-62@2.8 GHz, The Linux box is actually less powerful. I find your product very good for doing normally tedious tasks due to ease of use, but has a way been found yet to break this cap WinSCP seems to impose on me? I would really like to know what's going on since some that complain of slow transfer still get better than me. Any input is appreciated.

Hi @martin – have you go any thoughts for me? Cheers

@ktmarv: Hi – what Secure Shell SFTP client are you using? (I'd like to try it as well).

I tried forcing it to use SSH-1 which automatically then used SCP and Blowfish – speed seemed about the same for the download although it seemed to take longer to authenticate and retrieve the directory listing.

@ktmarv: Can I please check – are you getting ~120KB/s or ~120kb/s (bytes/s or bits/s).

Also I'm setting the download as a background job with multiple (6) background tasks running at once. However in the status window it only shows a single download happening? Should I see more if there are more? What might be preventing multiple downloads?

Another data point:

I'm seeing slow WinSCP upload speeds (using SCP) from a system at a university in Iowa (US) to a 1and1 server hosted in (I believe) Kansas City, Missouri (US).

By comparison, using the Secure Shell SFTP client and and doing an SFTP transfer, I'm getting 300-500Kbps transfers. Is there a setting that caps SCP?

FYI: Running on a 3Ghz P4 w/2.0GB RAM.
FYI: SFTP transfer caps out at ~120KB/s as well.

Thanks,
-kevin

3.8.2 (build 330) SFTP (allow SCB fallback)

What version of WinSCP are you using? What protocol? SCP or SFTP?

Hi,

I'm located in New Zealand accessing a server in Germany (I think - its a 1and1 server purchased through 1and1 UK).

Now at the moment I'm getting between 5,000 & 10,000 B/s transfer rate. So to put that in context I've transfered 60MB in 2 hour 21 minutes.

Now that seems a bit slow...

I did a speed test between here (New Zealand) and London and got 782kb/s download and 270 kb/s upload.

My processor doesn't seem to be doing very much...

Note: If I download less files they seem to come down quicker? I downloaded 2 large files and got up to 100,000B/s. Does downloading lots of small files add a lot of additional overhead?

Is there anything I can try/check/change?

Any help gratefully received.
Dale