Mirrorview Write Intent log - ok but what size???

We have 2 EMC AX4-5 SAN and we bought the Mirrorview software to replicate ours LUN on the second SAN, like a DR site. My question is, we should configure the Write Intent Log and this option need 2 LUN to work, but I dont see any documentation about the minimum LUN size for theses logs.

So what's the LUN or disk size that Write Intent Log need ?

Thanks