public long getDiskStoreSize() {
        try {
            return cache.getDiskStoreSize();
        } catch (Throwable t) {
            throw new CacheException(t);
        }
    }
Returns the size (in bytes) that this EhCache's disk store is consuming or <code>-1</code> if
that number is unknown or cannot be calculated.

@return the size (in bytes) that this EhCache's disk store is consuming or <code>-1</code> if
that number is unknown or cannot be calculated.
support/ehcache/src/main/java/org/apache/shiro/cache/ehcache/EhCache.java