Virtualized SANs help disaster-recovery budgets
Successful disaster recovery planning for storage administrators starts at the same place nearly everything else does, with a budget. In the case of storage disaster recovery the budget lets you match the costs of not being able to access various classes of data against the costs of providing different levels of availability.
The first step in making such a budget is to divide stored data into classes and determine how much it costs when a class of data isn't available. A virtualized SAN is especially useful in implementing a classification scheme because it makes it easy to 'slice and dice' the stored data according to the criteria and assign each classification to a separate virtual volume or series of volumes.
Typically the results of not having data available will range from stopping the enterprise in its tracks in the case of something like a critical OLTP system to very little in the case of little-used archives.
Careful classification is important here. Although it's best to have just the right number of data categories, in the initial planning stages it's probably better to have too many rather than too few classes. The classification scheme will probably be revised as you get further into the budgeting process in any event. Pay special attention to data dependencies that require 'less-important' data to make more important data useful.
The next step is to find out how much it will cost to make data available using different methods. Since there are a broad range of methods and associated costs, from having a fully staffed mirror data center in constant operation to having weekly backup tapes stored off site, it's important to match the costs of disaster recovery to the costs of being without data.
The third part of the process is deciding how much the enterprise can spend on disaster recovery and then getting the best possible value for your disaster recovery dollar.
Sun Microsystems describes the process of drafting a disaster recovery budget in a white paper titled: "Disaster Recovery: What's Your Plan" which is available at: http://www.sun.com/storage/wp.html.
Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.
This was first published in February 2002