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