SANs On The Internet: Meeting The Challenge.

This article is the second in a two-part series. The first part appeared in the June issue of CTR.

To expand capacity, additional storage can be hot-plugged into a SAN without taking any server resource down. This allows the provider to quickly respond to sudden increases in web access without disruption. It also facilitates the introduction of new web content, since new data can be added directly via the SAN and, then, enabled for servers when appropriate. Unlike parallel SCSI cabling, Fibre Channel SANs pose no physical restrictions for the amount of storage that can be added. Apart from bandwidth considerations, terabytes of content can be implemented on a single SAN. SSPs, in particular, require capacity in the terabyte range, since they may service multiple clients in a single zoned SAN configuration.

High Speed Storage Access

Current implementations of Fibre Channel offer shared (arbitrated loop) or dedicated (switched fabric) 100MB/sec (200MB/sec full duplex). This is a significant increase in throughput over legacy connections and will increase to 2Gbps (400MB/sec full duplex) by the end of 2000. To accommodate bursty traffic patterns from end user requests, it is essential that storage throughput does not become a bottleneck. Unlike multiple storage devices on a single SCSI string, switched SANs can deliver full bandwidth to every device. As hits increase, bandwidth is available on demand for servicing requests.

Shared Storage

Storage consolidation offers a number of benefits, including ease of deployment and reduced administrative overhead. As larger disk arrays are substituted for individual disks, the number of potential points of failure are reduced. High availability features engineered into some large storage devices provide additional security against loss of data access. The key driving force for shared storage, however, is reduced cost of storage administration. With fewer units to manage, an administrator can monitor more storage more efficiently. This is a compelling justification for SSPs. Enterprises are finding it difficult to recuit and retain technical personnel and face growing administrative costs as their storage requirements increase. By centralizing storage services and employing more efficient arrays, SSPs can maximize utilization of shared storage and rationalize storage administration. The enterprise can off-load all or part of their storage administration to the SSP, while the SSP can leverage in-house exp ertise to manage the resources of multiple clients.

Likewise, ASPs can deploy large arrays to house enterprise applications served up by the SAN. The ability to partition terabytes of storage for separate applications and yet minimize storage administrative overhead helps the ASP to reduce costs, which, in turn, makes the service more attractive to customers. If the ASPs' value-add is expertise in enterprise applications, keeping infrastructure overhead to a minimum is highly desirable. The efficiencies SANs enable make this possible.

Support For High Populations Of Devices

The address space for Fibre Channel fabrics is over 15.5 million devices. In practice, SANs are currently deployed with much smaller populations, typically 10 to 100 devices. Large enterprise SANs may require connectivity of thousands of devices, which becomes possible as backbone and departmental switches achieve interoperability. For Internet, ASP, and SSP applications, the ability to support l00s or 1,000s of devices on an extended SAN is attactive for backup purposes. As more storage can be brought under a single architecture, large tape libraries can be used more effectively.

Flexibility In Server And Storage Placement

For service providers, real estate is always at a premium. Organizing the placement of servers, storage and backup resources is facilitated if devices can be deployed without thought for cabling restrictions. Servicing and administration of storage, for example, is more cost effective if arrays can be centralized and not interspersed with adjoined servers. For large tape libraries, it may be impossible to make a common resource available via traditional SCSI cabling simply due to distance limitations. Fibre Channel SANs remove this obstacle and allow the service provider to place equipment according to business, not cabling, needs.

Data Security Via Tape Backup 

As with enterprise networks, tape backup is a persistent problem for Internet-based businesses. As the amount of content grows, the amount of time available for backup (the backup window) shrinks. This is such a truism today that many enterprises simply do not back up all of their data. SANs provide the optimal solution for backup, since backup traffic is moved off the LAN (where the bottleneck exists) and onto the SAN (where bandwidth is readily available). Backup is also a severe problem for service providers that utilize Network Attached Storage (NAS) for data access. Vixel's solution is to build a SAN behind the NAS servers to off-load backup traffic. In conjunction with Network Appliance, ATL, Spectra Logic, VERITAS, and Legato, Vixel has engineered a NAS/SAN configuration that allows multiple NAS filers to share a common tape resource over the SAN.

As shown in the Fig, user requests for data are carried over the messaging LAN network, while large block transfers for backup are off-loaded to a switched SAN. This configuration frees LAN bandwidth for content serving and enables the provider to safeguard both content and customer information against loss.

Managing Internet SANs

While a SAN infrastructure provides the plumbing for more efficient use of web, application, and storage resources, stability of the network can only be secured through SAN management. Device managers supplied by each SAN vendor address part of the problem, but at the expense of administrative overhead in maintaining multiple management platforms. In multi-vendor environments, monitoring HBAs, hubs, switches, FC-to-SCSI routers, servers, and storage arrays is feasible only if an integrated, heterogeneous management platform is available.

The rapid growth of the Internet and the increasing sophistication of Internet content place ever higher demands on storage access. Fibre Channel SANs address these needs by enabling availability, capacity, bandwidth, and deployment requirements that cannot be met by traditional means.

Tom Clark is the technical marketing director at Vixel Corporation (Bothell, WA) and the author of Designing Storage Area Networks: A Practical Reference for Implementing Fibre Channel SANs (Addison Wesley Longman).