It looks like since ext/memcache-3.0.3 the extension serializes and unserializes the given values. So the capabilities you provided for >=3.0.3 are OK but the one for lower versions have to be the same as for other not serializing storages (https://github.com/zendframework/zf2/blob/master/library/Zend/Cache/Storage/Adapter/Filesystem.php#L1153) ... Did you test `array` and `object` ?