what is "cachecard"?

Cache Card or Cache Module.is nothing but the Battery Backed Cache Module in AX100 & Ax150.

The AX150 houses a 256 MB Battery Backed Cache Module (BBCM) is socket attached to the Storage Processor.

It is used to protect the data that has not yet been committed to a disk surface, in the event of a hardware failure. This represents a mirror image of the write cache on the Storage Processor card. It has 2 lithium ion batteries with a 72 hour time limit and a 3 to 5 hour recharge time. It is equipped with three (3) LEDs, which are visible through the Storage Processor air dam. The Blue LED (left-most) indicates that data is stored in cache when the LED is illuminated. The Amber LED (center) indicates a fault condition. The Green LED (right-most) indicates fully charged batteries when illuminated solidly, and charging batteries when blinking. A graceful power down de-stages the cache data to the vault drives, so the BBCM is not needed and the batteries are not discharged.

You mentioned, the command is not working on CX4-960, Want to know why? Refer NaviCLI Admin Guide - Page Number 641. You'll see N/A for all the Series as this component is in AX100 & AX150 only.

If you are more curious about AX 100 & AX150 You may want to visit: http://www.emc.com/microsites/clariion-support/ax150/support.esp