MSA2050 unable to add disk group

Hello,

I'm unable to create a new ssd diskgroup, i get the followinf error message :

"a performance tier cannot be added to a virtual pool that contains a read cache"

i have currently 4 diskgroups:

1 dga01 and rca1 in pool A , rca1 is just an SSD drive used in read cache

1 dgb01 and rcb1 in pool B, rcb1 is an SSD drive used in read cache

I installed a tiering licence on the system.

now i want to add a new disk group with 12 SSD drives and i get the error message.

How can i use this 12 new SDD drives in a new volume and leave the other's as they are ?

Thank's

Gérard