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#1 2020-07-25 16:15:05

Registered: 2007-12-10
Posts: 95

Slow SFTP with Krusader (compared to SCP/SFTP shell)

This topic is fairly similar to an old one we have in the forum.

In short, I am testing currently available openssh (8.3p1-3) to transfer a large file (>2GB) between two machines, the storage being on TMPFS on each side. The network is regular 1gbps, with 3 switches between the machines and RTT about 0.22 ms.

On both SCP and SFTP shell (upload using "put"), the link is used almost to full capacity, the XFCE generic monitor shows about 979 mbps upload on the NIC at the source side. SCP reports about 110-112 MB/s, and I am happy with that, because I did not need to apply any trick such as those in the wiki.

However, when using Krusader via sftp://, the speed falls dramatically, and the link is loaded with no more than 390 mbps, with krusader reporting about 42 MB/s. I checked the "calculated window size" on Wireshark, the TCP receiver (when using Krusader as client) indeed advertises a much lower value (694528 vs 1963904, the ratio matching the throughput decrease to a good extent). But whether or not this is caused by the TCP layer itself or by a bottleneck on the ciphering, I cannot tell.

As a workaround, I mounted the same directory via SSHFS, and Krusader can copy the file at much higher speed (almost comparable to SCP).

I found a bug report on libssh which looks very much like my issue, but it did not mention  which version of libssh should contain the fixes.

I've grown fond of Krusader and would not like to switch application when having to transfer files between machines. Perhaps some automounting could alleviate the problem, if possible to use together with the bookmarks part.

Before thinking about opening something on the libssh bug tracker, I would like to ask if anyone has had a similar problem recently with krusader or dolphin.


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