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Serial port output to file high latency

I have a requirement to collect live serial data from a file in real time, the test is being redirected to an external hardware device but we also need to retain the file as a log.

The setup is pretty straight forward in the virtual machine setting I just set the serial port to use an output file and use tail to redirect the text as required. This all works but there is a real latency problem, VMware seems to write to the file in bursts like its doing some sort of buffering, the text sometimes takes 20sec to hit the file, other times its quite quick.

Is there any settings that have a bearing on this in say the advanced setting or vmx file.

Background info Environment: vSphere 5.1, tried writing file to local VMFS, NFS and ISCSI storage with all the same result, using serial to named pipe or TCP method doesn't have this same problem.

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