Dell H310 RAID controller card firmware as shipped by Dell on the R420 server does not support hardware IOMMU as claimed in the server specs. This means that this server is not suitable for smartserver deployments in its current form once the 3.1 release goes out.
OnApp and Dell are trying to resolve the issue regarding hardware IOMMU. This has been firmly tracked down to a RAID controller firmware issue on the Dell R420 and Dell are currently trying to resolve this.
Replacing the H310 raid controller card with the H710 controller card seems to resolve the issue. Check the current status of the issue with the Storage team before suggesting that to the customer.