I want to transfer a large file via pscp.exe from my Windows Host to a Linux VM. Before you ask I can't use Clip Board or Shared Folders because it needs to be automated.
The Hardware should be good enough, and also the VM has enough resources allocated to it.
But then sometimes the Speed just steadily declines like this:
Do you have any idea what the issue could be?
1 Answer 1
The problem occurs after the putty 0.67 client version, from 0.68 onwards with the pscp / psftp clients. I have had this issue for a while, however I was able up until recently to keep using 0.67 for file transfers. We are now upgrading from OpenSSH 8.3 to 9.9 at my work, and the latest 0.83 client has this issue still. A partial workaround is to add a -C for compression, for me this seems to produce a speed of around 6mb/sec consistently for file transfers.
Switching to winscp for file transfers, this scp / sftp client does not have this bug, I achieve around 70-90mb/sec file transfers to the same OpenSSH 9.9 service, that pscp and psftp struggle with, they start at around 20-30mb/sec and then drop gradually down to around 300-400kb/sec.
It seems like something to do with buffering of the file transfer for large files, or it could be network packet size throttling. Whatever the change that causes this bug it was introduced in Putty 0.68 and later.
I haven't tested the pscp and psftp clients at home with OpenSSH to see if its something network specific at work, but thats something I was thinking of trying. I was also going to see if I could report this to the developer, since its now something I need fixed.
Hope that helps - the little work around with -C as a parameter to the pscp or psftp client (-C = Compression), or the winscp.com client.
The reason I need to go to a newer putty client is because of supported and unsupported ciphers - https://superuser.com/questions/1642338/putty-fatal-error-couldnt-agree-on-host-key-algorithm (Quote from post) - ECDSA signatures (ecdsa-sha2-nistp256) need at least PuTTY version 0.68, while the RSA-SHA2 methods (rsa-sha2-*) will only be available in the next PuTTY release (0.75).
We are using RSA-SHA2 keys now for OpenSSH 9.9, ECDSA signatures for OpenSSH services, so I can't stay on 0.67.
I've just sent a bug report to the developer via https://www.chiark.greenend.org.uk/~sgtatham/putty/feedback.html - the email address at the bottom of the page, but there's no guarantee as its freeware of any resolution, we can only put the issue to them.