Smart networks: embedded devices and intelligent storage. (Storage Networking).
There are several ways to dissect a SAN. A common approach is to think of it as two layers: a physical layer with subsystems, NAS appliances and interconnect technologies, and an application layer that manages, protects, and provides access to storage resources and stored data. The hardware layer largely controls speed, performance and scalability, so adding virtualization and policy intelligence at this level would allow the SAN to operate storage pooling and application provisioning quickly and efficiently. But the reality is that embedding intelligence in SAN hardware components is an awkward process. SAN data paths traditionally follow a master-slave model between the host and its attached storage devices, which are most often RAID subsystems. The subsystems are expected to wait for instructions and incoming data from attached servers, and only swing into action when they receive the data. Hardware-based storage control is more reactive than proactive, as storage administrators use zoning and LUN masking to protect subsystems from warring servers. (Think of it as Server Wars: In environments where two or more servers use the same subsystem, Server A may try to grab every individual disk for itself, or Server A and Server B may blithely overwrite each other's data on the same disks.)
Role of Intelligent Switches Has Grown
Given the master-slave architecture, most storage vendors concentrate on managing storage at the software (host) level. But in spite of these inhibitors, there is a promising development around intelligent switches. Embedding intelligence in physical layer switches would move SANs from a shared storage architecture to more dynamic switch-based architectures. These switches operate now at the individual subsystem level, and in 2003 promise to operate over the entire storage area network.
The intelligent switch dates back to the 1980s, where it first appeared in voice networks. It became active in data networks during the 1990s, where it automated functions and eventually morphed into sophisticated routing switches. Within the storage network, vendors hope that intelligent switches will eventually help the SAN to evolve from its present shared model-where hosts share their attached targets on a limited basis-to a policy-driven, virtualized switched network. To accomplish this, intelligent switches are combining switching architecture with I/O routing intelligence.
Switches are already crucial to storage network fabrics, and serve as edge devices that provide connectivity across multiple networked devices. But as so-called Layer 2 devices, they cannot sense or control higher level functions on the application layers. However, just as data networks evolved from Layer 2 switching to Layer 3 and then to full-fledged routers, so storage network switching is adding intelligence to the storage mix. Intelligent switch development is producing both intelligent switches embedded in individual RAID subsystems, and in mega-switches that can intelligently manage arrays across an entire fabric, providing virtualization and policy-based services. (These switches are not meant to replace storage management software, but to enhance it. They will be able to apply software-based policies and virtualization across zones while efficiently utilizing existing bandwidth.) The Gartner Group expects SAN switching products to grow from approximately $1.2 billion in 2002 to $4.3 billion in 2006.
RAID subsystems share the SAN with JBODs and tape libraries. But RAID arrays comprise 90% of SAN storage devices and are at the focus of intelligent switch development. RAID arrays house their disks behind a controller card that manages server requests. But RAID arrays have limitations centered in I/O issues. When a server issues a command, unless it is served in the cache it travels Out of the server's HBA and through the network until it reaches the target subsystem. The request enters the controller which then connects the appropriate disk, retrieves and processes the data, then sends the completed data back to the requesting server. Since multiple requests may be hitting the array at the same time, the array-even with dual controllers and multiple channels-is still subject to a single internal bus. This can lead to data latency and serious congestion under heavy I/O conditions.
One approach to solving this problem is to embed intelligent switches in the arrays that take over the data routes into the RAID subsystems. Another approach is to place intelligent switches into the fabric to accomplish storage network-wide switching abilities and virtualization. Both subsystem manufacturers and switch vendors are active in this market. Pirus's PSX-1000, for example, works within the fabric instead of at the edge, allowing storage administrators to reconfigure storage network file servers on the fly. The switch works with traditional Fibre Channel switches and supports multiprotocol convergence, including storage based on SAN (block), NAS (file), and IP (iSCSI). For internal RAID switching, Hitachi Data Systems (HDS) uses its Hi-Star internal switching architecture to combine disk, cache and server interfaces. This results in high internal bandwidths and capacity on subsystems such as its high-end Lightning series.
Injecting New Blood
A flurry of acquisitions is also supporting intelligent switch introductions. Brocade recently acquired Rhapsody, which made multiprotocol switches with virtualization capabilities. Brocade's move was in response to Cisco's earlier acquisition of Andiamo Systems. The acquisition, which gave Cisco access to the lucrative switch market, granted an intelligent storage switching platform that Cisco markets under the MDS 9000 family. The multiprotocol switches offer both network and storage intelligence, such as IP traffic management and third-party storage virtualization support.
Vixel also concentrates on intelligent switches, and believes that shared loop backend models are inhibiting the growth of more reliable and easily managed switched systems. Brian Reed, senior director of business development at Vixel Corporation, said, "Using embedded storage switches to implement a switched back-end architecture delivers a solution to some of the most vexing and costly serviceability issues faced by storage providers and end-users alike. Since this technology can now be cost-effectively implemented, it's a fundamental next step for RAID, NAS and super-scalar system providers to move from shared to switched back-end architectures." Vixel depends on the switching architecture it calls InSpeed, which couples a non-blocking crossbar switch with loop port logic.
Like HDS, EMC has concentrated intelligence in its storage array controllers. But it is not developing intelligent switches along the same fast path, preferring to concentrate hardware intelligence in the controller. EMC says it will consider adding intelligence to intelligent switches to redirect I/O, but this would not be a replacement to controller- and server-based storage management.
Veritas supports intelligent switching but believes that the intelligence should be software-based, and sells SANPoint Control to switch makers and subsystem manufacturers. An advantage of a software-based approach is heterogeneous environment support--by using switches that use Veritas software, users avoid hardware vendor lock-in. Rajesh Radhakrishnan, director of product marketing at Veritas said, "As we start embedding capabilities into switches, things will get more manageable. Customers can look at distributed file systems throughout a company. The challenge is, how does it perform? How do you take that to the next level? The capability to embed software in switching devices in the network will take us to the next level."
A software-based approach can add excellent capabilities to switch-based intelligence. But according to Rick Walsworth, Maranti's director of product marketing, there are trade-offs with a software approach. A hardware-based approach can scale up to large enterprise data centers, since hardware performance is linear. Walsworth said, "It's difficult to achieve that same kind of scalability, that same kind of performance when you have to load everything into the processor first." The software/hardware question is not black and white, but depends on the nature of the storage environment and the business' needs. Software may be ideal for smaller--scale environments, while hardware-based intelligent switching may be better suited to large-scale enterprise storage containing hundreds and thousands of ports.
Array-based intelligent switches are in the market now, and network-wide intelligent switches with virtualization capabilities should hit the marketplace in the first half of 2003. As intelligent switches grow more--well, intelligent--they may have a far-reaching impact on the ability of SANs to dynamically manage and share large pools of storage over multi-vendor devices. By setting server levels specific to a particular application, intelligent switches will be able to prioritize high-end applications and assign appropriate bandwidth on a packet-by-packet basis. This allows for a much higher utilization of resources and can significantly lower the total cost of ownership.
Walsworth summed up, "What we're doing by bringing intelligence to the network is to have a higher level of consolidation through the infrastructure, but without sacrificing scalability and availability across the entire infrastructure."
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|Author:||Chudnow, Christine Taylor|
|Publication:||Computer Technology Review|
|Article Type:||Industry Overview|
|Date:||Nov 1, 2002|
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