Record IP Camera w/o motion detection or transcoding?

I have a suspicion (perhaps unfounded) that the motion detection and transcoding are adding a lot of complexity, and that's getting in the way of the recording reliability.

Hardware will always limit "reliability" and while motion detection is extremely unlikely too cause much of an issue, conversion from one format to another is almost always going to be hardware intensive.

As to the solution that would best fit the bill for your requirements, FFMpeg (here are some recommended Windows builds of FFMpeg) and some scripting/automation is probably your best answer.

FFMpeg is native to Linux, can potentially write the network streams to .mp4, can be started and stopped programmatically with scripting and supports a wide range of device including those that export H264.

Back of the envelope math says that a 2 Mbps stream is 22GB per day[...]

This article claims 15GB a day if the IR is recorded as black and white. It also seems to provide a good starting point for recording IP cameras on Linux with FFMpeg.