I was wondering if it is possible to share SAS disks with 2 systems, each system with its own DSS and RAID controller to have them in an active/passive or active/active configuration. This way there's no need to do replication, as they both use the same disks. I understand the advantages of replication, but at this moment, that's not what I'm looking for.
In DSS - no. In vanilla Linux, yeah. But there are some stipulations. You probably need EVMS and a private container and + Heartbeat2 to failover the resources. But EVMS is old and not being maintained any longer (I think it's dead) so I don't know if you want to put your eggs into a rotting basket. But even with EVMS - I think there are some issues with RAID'ed disks. Oh and don't even think about trying to use a SAS RAID controller for this.
Because there is no support for clustering with SAS RAID controllers yet. If an array becomes degraded, which controller does the rebuild? What about consistency checks? This is why the medium to high end systems have the RAID controllers built into the storage controllers.