It's your volume geometry that cannot be satisfied. Available space has to have characteristics that can be clearly matched to the allocation requirement. You seem to have space, but it's scattered and not a good candidate for such a "hail-mary" allo...
You don't mention any versions. But this sounds like a case I worked recently: you need 5.0MP1 RP1Incidents from 5.0 MP1 + 597517 + 936419 VxVM 5.0 MP1 Rolling Patch 1 (124361-01)VxVM 5.0 MP1Solaris 8,9,10
Budget considerations seem to trump all other concerns, in most Exchange environments. To replicate a transaction intensive application like exchange, the WAN interconnect will more likely be the limitation.(Just a guess so far, as the only dimension...