It is perfectly normal when buying HDDs/ SSDs (either for computers or in devices like PVR’s that even though it is advertised has having a certain capacity like 1TB or 2 TB etc, etc, the total available for writing to will be less than advertised as the HDD/ SSD reserves a certain amount of space for its own software which manages the disk.
So now that you know that this is not an issue, sit back and let the Aura entertain you with its eccentric behaviour, which you can read about in these pages. Good Luck.