If you're /var/lib/yacy partition is a LVM logical volume then why not just extend the size if space is the concern?
You can read more about LVM here: https://wiki.ubuntu.com/Lvm
$ pvdisplay # display all available Physical Disks
$ vgdisplay # display available volume groups
$ lvdisplay # display all logical volumes
The easiest way to increase the size of your logical volume is to first increase the size of the VolumeGroup where the logical volume belongs.
Example
$ sudo vgextend VolumeGroupName /home/somwhere/partition # Extend the size of the volume group to /home/somwhere/partition
Once you got your volume group extended, you can re-size the logical volume of interest
$ sudo lvextend -L +10g /var/lib/yacy # This will add 10GB to /var/lib/yacy
Reboot for the kernel to recognize the logical volume increase or use resize2fs command to resize logical volume on the fly.