2009
|-- 01
|   |-- 01.xml.gz
|   |-- 02.xml.gz
|   |-- 03.xml.gz
|   ...
`-- 02
    |-- 01.xml.gz
    |-- 02.xml.gz
    |-- 03.xml.gz
...

2009.tar.gz      # contains whole year
2009.tar.gz.asc  # gpg signature to verify data integrity