Hi Mario, to my mind using a symbolic link to move your YaCy data folder is a safe option, furthermore if you consider that on Debian the DATA folder is already distributed as a symbolic link between /usr/share/yacy/DATA and /var/lib/yacy.
I just checked on a Debian YaCy peer that the following steps works properly :
- stop the YaCy peer
- copy the data folder and important, keep ownership to yacy user (-p option) : cp -Rp /var/lib/yacy /newPart/newFolder
- rename the existing data folder to keep it as backup : mv /var/lib/yacy /var/lib/yacy.back
- make a new symbolic link to your new data folder : ln -s /newPart/newFolder /var/lib/yacy
- links chain to the data folder should now be : /usr/share/yacy/DATA -> /var/lib/yacy -> /newPart/newFolder
- start your peer : you should find your settings and indexed data unchanged. Hopefully the new partition freed disk space is also successfully taken into account : this step worked for me on Debian.