Its more of a pseudo-active/active than a true active/active like a Symmetrix.  Check out EMC166261 for some information on it.  In "failovermode 4," both storage processors (SPs) will report that all non-owned units exist and are available for access (Inquiry Peripheral Qualifier code 0x00). If the SP is in the process of shutting down, an Inquiry Peripheral Qualifier code of 0x01 will be returned. In addition, both SPs will accept and process media access commands to the logical unit. Internally, the logical unit is still owned by one of the SPs. The non-owning SP will internally forward the media access operation to the owning SP for processing. As a result, the array operates in what is termed an “Asymmetric Logical Unit Access" (ALUA) mode of operation. The owning SP will process commands more quickly and efficiently and is thus referred to as the “optimized path.” The non-owning SP will process commands less quickly and efficiently and is thus referred to as the “non-optimized path.” The optimized path is driven by LUN ownership, which can be changed in one of four ways in Active/Active mode: The Auto-trespass setting of the logical unit is ignored in this mode of operation.
clariion CX4 flare 29 support SCSI-3 ALUA mode. detail is in "[URL]", so can i say CX4 is a active/active array now?
CLARiiON is not a active/passive array any more?