Performance and quality of service increasingly make n-port ID virtualization a critical technology underpinning what vendors and users are building on to virtualize mission-critical applications and bring best-in-class management to the virtual data center.

Server virtualization is rapidly gaining market acceptance for server consolidation and provisioning. The concept of pooling resources to extend their use is common to many human endeavors: it is leveraged in business, fiduciary currency in economy, and virtualization in information technology. The complexity of sharing multiple resources across multiple users is masked by creating virtualized resources or virtualized users. Virtualization also delivers transparency to applications that have been designed to interface to a single user or resource. Over time, virtualized resources have included virtual memory, virtual storage (provided through appliances or embedded in controllers of enterprise arrays), and virtual networks or VPNs.

Server virtualization provides the ability to deploy a discrete number of full-featured application environments called virtual machines or guests on single or multiple hardware platforms. Hardware resource scheduling and management is run behind the scenes by a hypervisor, a user-invisible operating system. Server virtualization promises, and is starting to deliver, benefits that meet important user needs such as:

• Server consolidation yielding an increase in server hardware utilization. Analyst research confirms that server utilization, typically as low as 20% for separate servers, can increase to as much as 75%-80% on a virtual server. This reduces the overall number of servers required for an equivalent workload and enhances return on server investment
• Reduced management and maintenance overhead in direct relation to the reduced number of hardware platforms (freeing up the IT staff for more productive tasks such as new application deployment)
• Cost-effective test bed deployment of new applications
• Faster provisioning of new applications, which only require setting up a new virtual machine using available server, network, and storage resources
• Easier incident resumption and disaster recovery, as the virtual machines are readily portable to alternate hardware resources.

Figure 1 Virtual port attachment using NPIV

These benefits explain why analyst firms such as Gartner have rated server virtualization as one of three disruptive technologies that will change the face of IT (the other two being blade servers and Linux).

There are two different breeds of virtual server environments. Initially, virtual servers were introduced on very large mainframes to marshal extremely powerful multiprocessor, memory, and I/O resources. In such an environment, virtualization provided a way to create smaller chunks of servers for specialized or transient use.

A different, increasingly compelling model consolidates environments onto farms of standard servers. The benefits here include resource management, flexibility, and workload portability. Many third-party vendors are also adding enterprise production-oriented value and management software.

The Emergence of N-Port ID Virtualization

Consolidation servers and virtual servers are located mostly in the main data center and draw on enterprise storage resources. Virtual operating environments such as VMware already enjoy a very high SAN attach rate. The portability and recovery capabilities of these environments rely on external shared storage and are most effective in a SAN connectivity environment. In addition, the high performance delivered by the Fibre Channel protocol is best positioned to serve the higher I/O requirements for the multiple virtual machines running on a single server. SAN connectivity helps enable server virtualization, while server virtualization drives an increased need for SAN connectivity.

Today's server virtualization solutions, combined with industry standards in the storage management space, are bringing further success to this growing market segment. The emerging N-port ID Virtualization (NPIV), in particular, provides the following benefits:

• The ability to use today's proven SAN management methods to associate a SAN-based storage device to a particular virtual machine. This allows the end user to manage this critical aspect of storage management with a common methodology across bare metal and virtual servers. In cases requiring virtual machine migration, this feature guarantees that access privileges travel with the virtual machine.
• The ability to provide in-fabric isolation among virtual servers and virtual machines. This isolation confines network events and device-specific behavior to the particular virtual machine. It takes the best practices in place in data center SANs today and extends their reach to the virtual server.
• The ability to selectively enhance application performance by applying fabric quality-of-service (QoS), array/LUN configuration options, and VM-to-LUN performance monitoring and troubleshooting
• Application-transparent HBA replacement, making provisioning easier and reducing long-term cost of ownership.

Still, adoption of virtual server environments is somewhat inhibited by the limited flexibility of storage access. All virtual machines on a physical server currently share the same external storage resources and a single set of Fibre Channel addresses provided via the underlying OS or hypervisor. This has several limitations:

• The absence of fabric zoning or array-level LUN masking keeps all storage potentially visible to all virtual machines, contradicting SAN best practices. The current remedy is to implement masking in the server itself by way of the hypervisor's file system. This solution is limiting due to its introduction of another server administrator-managed procedure and tool beside those in use by the storage administrator. Secondly, it scales poorly: rezoning for hundreds of servers only requires one central change, whereas server-level masking must be modified for each virtual server (besides zoning for traditional servers).
• Specific SAN resources can't be assigned by priority to mission-critical applications or virtual machines, which limits quality-of-service implementations
• One of the key features of virtual environments, the ability to quickly overcome hardware failures by moving virtual machines to alternate servers, is restricted and, in some cases, inhibited by the hardware-based Fibre Channel port addresses being lost along with the failed servers. Here again, users eager to enjoy the benefits of virtualization have a workaround, which is to implement open zoning for all virtual servers. This solution, applicable when the role of the virtual server is limited to non-critical file-and-print server consolidation can't be deployed for mission-critical workloads where zones are used to enforce application and server isolation.

The fact that server virtualization is highly successful under its current storage-attach restrictions testifies to the benefits and potential of this technology. Removing these limits will enable new classes of applications, fuller data center integration, and accelerated virtual server deployment. This will be accomplished with NPIV.

NPIV Coming of Age

NPIV is an ANSI T11 standard describing how a single Fibre Channel HBA port can register with the fabric using several worldwide port names (WWPNs). Upon brought up, the HBA first logs into the fabric (FLOGI) then requests (through ADISC) as many fabric IDs from the switch as it has logical ports, identified by unique WWPNs. The fabric will then route messages, display topologies, and monitor the status of these virtual endpoints as it already does for the physical ones.

The use of multiple addresses through a single HBA port is very valuable in virtual servers since it enables zoning and LUN masking, giving each virtual machine specialized access to only its required storage resources. In addition, exclusive assignment of buffer resources to priority virtual machines through their "port" provides added granularity to fulfill SLAs. Finally, the ability to "tear down" a virtual port and reinitiate it on a different server greatly enhances virtual machine portability for load balancing, portability, and incident recovery. In short, NPIV enhances SAN connectivity, flexibility, resource allocation, and recovery.

NPIV requires two capabilities:

• The HBAs firmware and the proximate switch must be able to negotiate several addresses. This is specified as part of the ANSI T11 Fibre Channel standards and is available on the latest fabric switches from many leading vendors.
• The driver must be able to accept requests from the operating system (in the case of a virtual server, the hypervisor) to create, modify, and delete Fibre Channel addresses, and provide status on each address (status, health, throughput, event history). Support for N-Port ID virtualization is now provided in the VMware ESX 3.0 and 3.5, Microsoft Virtual Server and Hyper-V, Linux (Citrix, Red Hat, Novell, Oracle) and Solaris environment, with a growing number of management tools offered by OS vendors and HBA providers.

Summary of Benefits for N-Port ID Virtualization

Overall, NPIV lets customers effectively virtualize the HBA functionality so each virtual machine running on a server can independently access its own protected storage. Specific performance and reliability benefits include the following:

• Mixed Workload Performance: Multiple virtual machines typically generate a mixed workload flowing through the same physical adapter(s). By implementing flow control at the frame level, and not just at the sequence level, the firmware will avoid situations where a large block request (e.g., file transfer or database checkpoint) from one of the guest operating systems would monopolize resources and severely affect response to the smaller requests (e.g., online transactions). Frame-level exchanges avoid these situations and ensure that the overall throughput is maximized and each application or guest OS is served promptly. The concept of "fairness" implemented through frame-level exchanges maximizes utilization on SAN connectivity and enhances the benefits of server consolidation.
• Predictable Quality of Service: Frame-level exchanges introduce fairness in mixed workload by mitigating the impact of large-block background operations on mission-critical transactions for more predictable OLTP response times and QoS. Frame-level exchange technology becomes of paramount value in virtual servers as they are designed to support and encourage mixed I/O workloads, especially as they come of age and can re-host major ported applications and corporate database servers.
• Quality of Service in Virtual Server Environments: NPIV provides the technology infrastructure to apply end-to-end application-specific QOS capabilities in virtual server environments.

Besides the isolation and provisioning benefits already discussed, performance and quality of service increasingly make n-port ID virtualization a critical technology underpinning what vendors and users are building on to virtualize mission-critical applications and bring best-in-class management to the virtual data center.