All thin provisioning is not created equal

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What about performance? There are differences in how an array's architecture affects the performance of thin-provisioned LUNs, specifically how the system distributes data across the disks in the thinly provisioned pool. A Compellent system monitors performance and, if bottlenecks occur, the array can dynamically redistribute data to less-used disks. Hitachi has published whitepapers about how its thin provisioning can be used to increase performance for IOPS-sensitive apps when a single array or RAID group can't provide the required performance. In addition, some systems can enhance performance by "dedicating cache to specific pools," says EMC's Wambach.

"When a LUN or file system is created using thin provisioning, we contiguously pre-map where the LUN will grow," says Pillar Data Systems' Commins. The firm's Axiom management software, called Pilot, has an expert system that "finds the best place to lay out the next chunk given that LUN's performance priority and app profile," he adds.
How extensive are capacity management and reporting tools? This is probably the most important question, because you don't want an app to unexpectedly quit due to lack of disk space. Wambach says TP needs to integrate tightly with existing management and

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business continuity processes, but "not all offerings do this." It should also be simple and quick to add more capacity to a thin-provisioned pool, adjust the amount of host-perceived capacity and automatically add capacity when thresholds are passed. Eric Schott, senior director of product management for the Dell EqualLogic product family, adds that you should be able to convert data between normal and thin provisioning.

Other considerations include whether there can be different thin-provisioning policies on a primary site vs. a mirrored destination site, and across different tiers. And how good is the vendor documentation? NetApp's documentation, for example, has a section on the advantages and disadvantages of different capacity configurations for storing and deleting snapshot copies.