Unable to add shared disk to 2012 cluster

Hello, i have three shared disks coming from an IBM V7000.

All three disks are visible and mountable by both of cluster nodes but, adding them to cluster, i have:

disk 1) added as quorum device

disk 2) i am able to add it to the cluster

disk 3) i can see it in Server Manager - Storage and i am able to put it online on both servers but it is not present in the disk list when i try to add it to the cluster.

Cluster validation is successful (except for some warning).

Cluster nodes are virtual machines on ESX5.5 and i followed best practices about RDM compatibility configuration.

How could i debug the problem and try to understand where the issue is?

Any hint is appreciated.