The general rule is to round down, so you round down.

Unless you are told otherwise in the rules, D&D always mandates you round down. The Long rest section has no such exception (the only exception I've seen so far is for the wizard's spell recovery)

The only exception to this for HD is first level (even though, tbh, there is no rule that actually makes this excpetion) where you get a minimum of 1. (We only know this is the design intent because Mr. Mearls has said so).

The general rule is to round down, so you round down.

Unless you are told otherwise in the rules, D&D always mandates you round down. The Long rest section has no such exception (the only exception I've seen so far is for the wizard's spell recovery)

v.2 of BD&D now includes language that indicates a minimum of 1 HD is recovered during a long rest.

The character also regains spent Hit Dice, up to a number of dice equal to half of the character’s total number of them (minimum of one die). (p 67)