Tiered storage: does all data have to fly first class? - Storage Networking

Computer Technology Review,  Feb, 2004  by Tad Lebeck

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A practical tiered-storage strategy is best pursued in incremental fashion: Defining data classes and their associated tiers of storage service, then implementing policies and service delivery processes--one class of data at a time. This "crawl, walk, run" approach provides a low-risk, non-disruptive way to demonstrate immediate results while continuing to learn, adapt and improve. I break the initiative down into 3 phases: Service mapping, process mapping, and implementation. No matter which spin on these steps is right for you, always think big, start small and scale fast.

Service mapping defines the business requirements for your data, classes of storage services to meet these needs, and a policy framework to associate one with the other. Data should be classified as to requirements for availability, application performance, protection, recovery time, and retention time. Service tiers or classes should be defined to match these needs. The number of tiers, or granularity of service class to application requirements, varies. But as a general rule, it is best to start with a few (i.e., gold, silver, bronze) and then expand variety as you gain experience.

Process mapping defines the operational workflow, policy and systems operations required to ultimately match and deliver classes of storage to your data. These processes include initial provisioning, ongoing capacity and data management, as well as migration processes as data requirements evolve. Start with a process for a single data class for an application, and its respective storage service tier.

Map the end-to-end service delivery process--human workflow, system operations, and approval chain--all the way from the application (or service consumer) to the supporting infrastructure. Limiting your view of tiered storage to the SAN infrastructure ensures that LUNs of certain characteristics are "available" but misses the whole point of certifying that the right application actually receives its requested service in a compliant fashion. The end-to-end view typically involves not only operations performed by storage administration but systems, database and backup administrators as well. For example, adding space to a database on a new file system with mirrored storage, remote replication and tape backup is a process that spans all these departments, in multiple locations. Mapping all the local and remote operations, as well as the workflow and interaction between administrators, is the first step in being able to achieve compliant service delivery.

Define the control model: Who specifically is involved, who will have control over policy definition and process execution, for what infrastructure/operations in the service path? What policies do you want "fixed," or system enforced, and which one will humans make? What are the response times and escalation process for exception and error handling? The service delivery process and control model not only provide a detailed definition of how service delivery objectives are met, but should also be used as a baseline for process improvement throughout the implementation phase.