We have an Hylafax 5.2.5 CentOS 5 installation hosted inside a Xen virtual machine. It works quite well, but now I'm in the process of upgrading/migrating it to a KVM virtual machine running Ubuntu 10.04 and Hylafax 5.5.1 (compiled from source using http://sourceforge.net/projects/hylafax/files/hylafax%20debian%20build%20files/ )

The problem I'm having is that - while receiving works fine - sending faxes is extremely unreliable, I get lots of "No response to MPS repeated 3 tries", or "Failure to transmit clean ECM image data."

The line, modem and configuration files I'm using are the same as before, so I thought that it could be a KVM scheduling issue, but even setting cpu_shares to 10240 instead of 1024 doesn't change a thing... What else could I try?

Here's an example log file http://pastebin.com/cN01cpEs