After a few day-per-day hadoop ingestion tuning (using the CLI index hadoop), I decided to import my data month by month. No problem in the MapReduce phase, all went smooth, and data were properly generated for the whole month in HDFS:
1.4 K 2016-08-20 16:26 /tmp/hadoop_output/ds/20160701T000000.000Z_20160701T060000.000Z/batch-one-month/0/descriptor.json
284.6 M 2016-08-20 16:26 /tmp/hadoop_output/ds/20160701T000000.000Z_20160701T060000.000Z/batch-one-month/0/index.zip
Some segments were up to the GB (btw I forced numShards=1).