Some vendors certify their SAN storage-management applications on competitors' storage arrays. Such certifications ensure a basic operational level and management capability but don't ensure support for all functions. At press time, EMC and Compaq had gone the extra mile and agreed to cross-license their SAN APIs to allow more manageability between the two vendors' storage products.
Under its SANmark open device interoperability certification program, the Fibre Channel Industry Association (FCIA) develops test suites for Fibre Channel HBAs, switches, and end nodes (e.g., storage arrays, tape libraries, disk subsystems, Fibre Channel—bridge devices). The tests ensure that the products within each category can communicate with one another according to the ANSI Fibre Channel protocol standards. Currently, these tests don't test the interoperability of storage-management applications with hardware; however, the FCIA plans to expand the program in 2002 to include application/hardware interoperability. For more information about the SANmark program, see http://www.fibrechannel.com/sanmark/index.master.html.
The Convergence of NAS and SAN
Although NAS and SAN differed clearly in the past, new NAS products from Compaq and EMC are beginning to blur the lines between these two complementary technologies. Compaq's recently released StorageWorks NAS Executor E7000, for example, can leverage the storage resources in Compaq's StorageWorks SANs. The Windows-based E7000 comes with both Fibre Channel and Ethernet network interfaces. When NAS products share the SAN's storage resources, administrators can use the SAN's virtualization software to assign a portion of the storage pool to the NAS device (I discuss storage virtualization later). Thus, StorageWorks users can easily manage NAS and SAN storage, and the E7000 can benefit from the SAN's speed and scalability. This ability to use the SAN's storage arrays also lowers the E7000's cost (pricing starts at $47,000 for a two-processor configuration with 2GB of RAM) for companies that elect to use both Compaq's NAS and SAN products.
EMC has taken a similar approach with its enterprise-level EMC Celerra File Server. Like Compaq's E7000, the EMC Celerra separates processing and storage functions, leveraging the storage in EMC's SAN-based Symmetrix family of storage arrays. One of EMC Celerra's strengths is its high availability—in its most basic form, the product comes as a two-node clustered solution with two rack-mounted file servers and a control station that manages the servers. A Symmetrix storage array can cluster as many as 14 file servers sharing as much as 28TB of storage. But you don't need to invest in a SAN to use the EMC Celerra—EMC also sells Symmetrix and EMC Celerra together in the same rack-mount cabinet.
EMC also produces the EMC CLARiiON IP4700, which the vendor describes as a midrange NAS solution. The IP4700, which starts at $75,000, is an integrated NAS device with room for approximately 7TB of internal storage. Should you decide to implement a SAN later, you can convert the IP4700 into an EMC CLARiiON FC4700 SAN storage array by installing another version of the IP4700's proprietary OS and replacing the Ethernet interface with a Fibre Channel HBA.
Storage Virtualization
Storage virtualization represents the physical disk space from multiple arrays as one storage pool, thus letting you centrally manage data and share it over a network of heterogeneous servers. Virtualization lets you manage storage resources without requiring that you know the physical disk configuration. In addition to letting you assign portions of the storage resource to individual servers, virtualization lets you easily maintain backup schedules, reallocate storage among the servers, and quickly add new storage without bringing down the storage array and without concern about disk sizes, types, or configuration.
Both NAS and SAN vendors offer virtualization solutions. For example, Network Appliance claims that its NetApp DataFabric Manager can support hundreds of its NAS appliances. SAN vendors have offered host- and array-based virtualization products for some time. Host-based products provide a unified view of network storage but must be installed on each server. Array-based packages give each server a logical view of the storage assigned to it, but you usually must manage each storage array separately. One exception is XIOtech's REDI SAN Links array-based virtualization software, which presents a logical view of all SAN storage for the vendor's MAGNITUDE storage arrays.
The need for a unified solution that can scale up as you add new servers and storage arrays has focused attention on network-based virtualization solutions. HP recently introduced its HP Surestore SANLink appliance, which sits on the storage network between your servers and storage arrays and provides all servers a logical view of the entire network's storage resources. (SANLink sells for approximately $225,000.) HP has tested the product with storage arrays from Hitachi, Dell, LSI Logic, and EMC. Compaq also plans to offer a network-based virtualization product by midyear.
Different vendors define virtualization differently, so you'll need to ask questions and compare offerings before settling on a NAS or SAN provider. For instance, although virtualization products might let you assign storage to each server from one logical pool, can you move data from one array to another within the virtual pool without disrupting server access to the data? And does the virtualization solution truly mask the configuration complexities of the storage arrays?
The Future of Storage
Direct-attached storage is inexpensive in the short term but is difficult to manage effectively when you're adding servers and you have a small staff. A combination of NAS and SAN products makes sense for many organizations, especially if the NAS appliance can leverage the SAN's storage resources.
Throughout the past year, vendors have introduced 2Gbps Fibre Channel HBAs, switches, and storage arrays at prices only slightly higher than current 1Gbps SAN equipment. These high-speed Fibre Channel SANs are particularly well suited for use with performance-critical applications and applications that require assured delivery over distances of up to 10 kilometers. But creating an enterprisewide Fibre Channel SAN with thousands of servers might not yet be feasible. The cost of such a network would be extremely high, and creating the Fibre Channel switching fabric needed for such a large SAN would be technically difficult.
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