This level of high availability can be extended to file-based storage access by front-ending an EMC Symmetrix or HDS USP with a NAS gateway; for example EMC's Celerra NAS gateway can be paired with a Symmetrix. Not having its own NAS gateway, HDS offers a NAS blade for its TagmaStore USP that enables access to USP storage via file-system protocols.

To increase the availability in arrays that support file- and block-based protocols through a single controller, nodes are often clustered; if a node fails, another node takes over its workload. Clusters are available in active-active and active-passive configurations. With an active-active cluster configuration, it's crucial to design the cluster to cope with the reduced processing power in case of a node failure. The cluster configuration may also impact the amount of usable storage, a fact painfully experienced by Chalkley Matlack, senior network administrator at doeLegal LLC in Wilmington, DE, who replaced his EMC Celerra NS500 array with a Reldata Inc. storage system. "We weren't able to move the NS500 beyond 16TB without switching from an active-active to an active-passive configuration, giving up redundancy," laments Matlack.

Cluster options are available at the higher end of the performance and price product spectrum from such companies as EMC, Microsoft Corp., NetApp and Pillar Data Systems. Multiprotocol array clusters are the way to go in environments with 24/7/365 uptime requirements. "Availability was our primary concern when we chose NetApp 3000 series clustered arrays for all of our locations," explains Michael Israel, senior VP of information services at Six Flags in New York City.

Storage management
Managing the storage of multiprotocol arrays is more challenging than managing FC-only arrays, mostly due to the limited support of NAS protocols by storage management apps and storage standards. "SMI-S has been targeting the SAN market and paid little attention to file-system protocols," says Sean Derrington, Symantec's director of storage management.

Storage resource management (SRM) vendors have overcome this hurdle by directly integrating their suites with arrays from leading storage vendors, with NetApp enjoying the most extensive support among arrays supporting both NAS and SAN. For instance, Symantec CommandCentral 5.0 has been integrated with NetApp filers down to the file level across multiple filers and multiple locations. "We're able to monitor performance and capacity across multiple filers and locations using a combination of SMI-S and Data Ontap APIs, a capability currently only available for Network Appliance filers," explains Derrington.