Building the Data Warehouse

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Overflow Storage

Data in the data warehouse environment grows at a rate never before seen by IT professionals. The combination of historical data and detailed data produces a growth rate that is phenomenal. The terms terabyte and petabyte were used only in theory prior to data warehousing.

As data grows large a natural subdivision of data occurs between actively used data and inactively used data. Inactive data is sometimes called dormant data. At some point in the life of the data warehouse, the vast majority of the data in the warehouse becomes stale and unused. At this point it makes sense to start separating the data onto different storage media.

Most professionals have never built a system on anything but disk storage. But as the data warehouse grows large, it simply makes economic and technological sense to place the data on multiple storage media. The actively used portion of the data warehouse remains on disk storage, while the inactive portion of the data in the data warehouse is placed on alternative storage or near-line storage.

Data that is placed on alternative or near-line storage is stored much less expensively than data that resides on disk storage. And just because data is placed on alternative or near-line storage does not mean that the data is inaccessible. Data placed on alternate or near-line storage is just as accessible as data placed on disk storage. By placing inactive data on alternate or near-line storage, the architect removes impediments to performance from the high-performance active data. In fact, moving data to near-line storage greatly accelerates the performance of the entire environment.

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