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Data determines the right disaster recovery

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Sorting out disaster recovery options

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Click here for a worksheet about various disaster recovery solutions on the market (PDF).

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DR hardware platforms
There are four principle hardware delivery platforms: storage array, general-purpose server, purpose-built storage appliance and the intelligent storage networking switch. The storage array is a purpose-built storage server for block or file-based storage. Many storage vendors provide optional storage array DR software, which includes synchronous and asynchronous remote mirroring and snapshot. These software products are typically specific to the individual vendor and its storage offerings.

Storage array-based software usually doesn't require application server agents. The arrays are server operating system-agnostic and the DR applications run fast. They are also installed in thousands of locations, and are proven and mature.

However, the array DR applications don't work with heterogeneous storage. In general, they don't have file-level or application awareness. (Array applications with application awareness use agents.) Storage array IOPS and throughput decline while DR applications are running. And these DR applications are licensed and managed on a per-array basis. Storage array DR applications have some of the highest TCOs and, in some cases, consume more raw storage than non-array based alternatives.

General-purpose servers have very low acquisition costs and low TCO. Implementing, servicing and managing them are known quantities. Performance is tunable and DR application performance leverages ongoing improvements in server technology. Increasing performance or scalability may be as simple as buying the next-larger server, and more memory and processing power. Other advantages include support for heterogeneous storage, and application and file-system awareness. General-purpose servers require DR application agents.

The purpose-built storage appliance is nothing more than a DR application optimized server. A good way to think of the purpose-built storage appliance is to view it as a networked storage controller. It leverages technologies specifically optimized for storage DR applications. Optimization includes I/O performance, throughput, scalability and high availability (no single point of failure). TCO is definitely lower than for the storage array or intelligent server, but the purpose-built appliance is proprietary. It may also have higher initial acquisition costs and may not keep up with server technology advances.

The intelligent storage networking switch is a relatively new DR delivery platform. The storage area network (SAN) switch is the ideal system to provide DR applications because it sits between application servers and their target storage, and it also has visibility into all servers and storage targets.

There are two principle types of intelligent storage-network switches. The first essentially integrates the purpose-built storage appliance as a server blade into a Fibre Channel SAN switch or director. The second packages it as a storage software delivery platform that just happens to use switching as part of its architecture. It leverages a new technology called split path acceleration of independent data streams (SPAID). SPAID improves performance by separating the control path (the slow path) from the data path (the fast path). It enables out-of-band virtualization without requiring server agents and runs most DR software applications without any changes. Initial costs and TCO will probably be much higher than for non-integrated systems.

No other platform has the DR application performance potential of the SPAID intelligent storage networking switch. SPAID switches have an inherently higher level of reliability, availability and serviceability than storage appliances because of the separation of control path from data path. Unfortunately, there are only a small handful of products that use the SPAID architecture. These include software from Incipient Inc., Maranti Networks, StoreAge Networking Technologies, Troika Networks Inc. and Veritas Software Corp. Of these, only StoreAge has a comprehensive suite of DR applications that works with all of the SPAID intelligent storage networking switches. Maranti has its own suite of DR applications, and Troika is working on a suite with tie-ins to other software-based DR applications. Incipient and Veritas are currently limited to volume management only.

Remember, a cost-effective DR strategy requires a mix of DR applications running on several platforms. Managing cost and effectiveness requires matching the value of the data to specific DR capabilities. This mix-and-match approach will reduce overall DR cost while meeting the organization's needs (see Sorting out disaster recovery options). Of course, this process must be repeated periodically to re-evaluate new technologies, products, SLA requirements and compliance regulations.

This was first published in January 2005

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