Slow SCP Speeds

November 15th, 2005

When I reformatted my server and put Fedora Core 4 on, I had a marked decrease in transfer speeds. Before the format, i was getting about 3mb/sec, which although is slow over a 100mbit network, it was bearable. However, after the format, I had speeds on scp throttling at about 60Kb/sec!

The confusing thing was that transfers over http and ftp were going at about 9mb/sec, ruling out any hardware problems. After quite a bit of hunting around the internet, I stumbled upon an article that I've now misplaced the link for .

Anyhow, the fix is below.

Edit your /etc/sysctl.conf file to include the following:
net.ipv4.tcp_window_scaling = 1 net.ipv4.tcp_rmem = 4096 87380 16777216 net.ipv4.tcp_wmem = 4096 65535 16777216 net.ipv4.tcp_mem = 8388608 8388608 16777216
Restart your network:
service network restart

Et Voila… super fast scp speeds!

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