The importance of pre-ionisation for the non-chain discharge-pumped HF laser is studied through experiments on an X-ray photo-triggered laser using mixtures of Ne, SF6, and ethane. The discharge dynamic in Ne/SF6 mixtures or pure SF6, as well as the stabilisation effect induced by C2H6 and consequences for the laser performance, are investigated for pre-ionisation electron density values, neo, ranging from 106 cm-3 up to 109 cm-3, as well as for the so-called discharge self-breakdown mode. Without ethane, the minimum neo value which is needed to complete 100% homogeneous charge deposition in the plasma is a very sharply increasing function of the SF6 pressure. This hinders performance optimisation when the molecule used to react with F-atoms, for instance H2, has no effect on the discharge dynamic. The minimum ethane partial pressure that is needed to stabilise the discharge depends on neo, the pumping pulse duration, the deposited electric charge, and the SF6 pressure. Discharges in Ne/SF6 can be much more efficiently stabilised by addition of a small amount of ethane than by an increase of neo. A pre-ionisation density as low as 106 cm-3 is sufficient to achieve the maximum laser energy value, but total suppression of the pre-ionisation has a detrimental effect on the active medium homogeneity.