I'm using a separate storage for my graph data that is generated by RRDCached to minimize the usage of the local disk. The problem is that rrdcached won't start and fails with this message:
RRDcached has a built in symbolic link check that checks if the basedir (-b) is or contains a symbolic link, and this is not supported by the application. If you still need to have the basedir on a separate disk, consider using a bind mount instead of a symbolic link.
For further information, consult the rrdcached manual: