When IT managers store virtual machines on a storage area network, the typical option is VMware Virtual Machine File System (VMFS). For many applications, including file and print servers, web servers and enterprise resource planning applications, VMFS works fine.
But for processing-intensive applications such as SQL Server databases and e-mail, using VMFS can put too much overhead on the SAN. One approach used by the Navy Marine Corps Intranet is to use a technique known as Raw Device Mapping (RDM).
Jeff Smith, server manager for EDS, an HP company, which manages NMCI for the military, says Raw Device Mapping lets NMCI use the native file system on the storage area network to store the virtual machines.
“The best way to think about it is that RDMs are a way to more effectively use the space on the SAN and improve overall performance,” Smith says.
Smith says that although configuring RDMs is not especially hard, it does take someone who understands virtualization and the difference between RDM and VMFS. He says the need to use RDMs is one of the main reasons many agencies and other organizations have not yet moved to virtualize their sometimes numerous Microsoft Exchange servers.
“Most people just want to get virtualization to work and aren’t about to try virtualizing Exchange,” he says.
But that will change as more IT shops gain experience and their comfort level with virtualization technology grows. The potential cost savings and ease of management through virtualizing Exchange are too great for federal agencies to hold back, Smith expects.
Smith says virtualizing Exchange offers numerous benefits: