ok thxs both :-) I will probably exclude ./mails, ./cache, ./solr from my tar.gz file (and remove lucene).
The main purpose is to clean a little bit before xwiki version upgrade I confirm that "mails" and "cache" are tiny: # du --max-depth=1 -h ./ 448K ./mails 32M ./extension 4,8M ./lucene 3,8G ./storage 94M ./solr 8,5M ./jobs 1,9M ./cache 4,0G ./ Pascal
