AVRO will perform byte-aligned packing. e.g. if you have 64 bits storage but only require 28 bits you will use 32 bits.
+-----------------------+
| SLOW LOGGING |
+---------+-------------+----------+----------+---------------+----------------+
| signals | signal size | log rate | log time | total samples | avro file size |
+---------+-------------+----------+----------+---------------+----------------+
| 64 | 8 bit | 10 s | 1 hour | 360 | 0.03 Mbyte |
| 64 | 16 bit | 10 s | 1 hour | 360 | 0.06 Mbyte |