"It is not accessible to the card or the volumes on the card for use as a cache." it makes sense.
and thank you for the tip, I did get all the pieces, including the cap.
The reason that I bought 9270cv was my old 9260 was unstable for some reason, in MSM it gave "unexpected sense at address 0x....", and some disk went offline starting rebuild.
At first I suspected it broke. After mounting 9270cv, the warning message disapeared, but I did find that temperature of main chip was ridiculously high (96C, 204F).
Maybe my old 9260 didn‘t break after all, maybe it's just overheating.
I'll keep my case open for now, and wait for the mini fan I bought.
Thank you for the tip:"I think that any amount of cachecade wild be nice even if it were mlc. It helps buffer more read/write at faster seeks."
I'll post performance result when I buy ssd for cachecade.