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Thin provisioning

To use an airline analogy, thin provisioning lets storage admins "overbook" disk space by provisioning more disk space than an application is likely to use. The disk space is only actually occupied when the application writes data, leaving the unused capacity available to other applications, rather than sitting allocated but unused.

Just as the gate agent must keep a close eye on how many passengers actually show up, storage administrators need real-time monitoring tools so they know when to add more physical disk or expand the size of logical volumes if too much data shows up for "seats" on the array.

Using thin provisioning, External IT USA's Stedler has allocated 215 TB of space for his VMware servers, backed by only 5.5 TB worth of actual disk. He said he's very pleased with how DataCore Software Corp.'s SANsymphony provides real-time reports about "how much storage has been allocated … vs. how much has been claimed by a virtual machine," and how he can set thresholds for alerts when drives reach a certain utilization level.

Forrester Research's Reichman said NetApp has "decent capacity visibility with their Operations Manager tool that's designed to report on NetApp-specific storage," but faulted the company's SANscreen for lacking visibility to the file-system level. He also faulted EMC's Ionix ControlCenter and IBM's Tivoli Storage Productivity Center Suite as lacking the detailed reporting needed to support

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thin provisioning, and said "none of the big SRM [storage resource management] tools seem to have hit the nail on the head … and I think it's a big reason why users are slow to adopt thin provisioning."

Reichman and other analysts singled out smaller companies such as Compellent Technologies Inc. and 3PAR Inc. as providing such detail on their own platforms, helping drive faster adoption for them.

On the higher end, Gartner's Cox said he's gotten "good feedback" from customers using Hitachi Data Systems' Universal Storage Platform V and Universal Storage Platform VM storage controllers. In general, customers are reluctant to risk the availability of their high-end systems with new technologies such as thin provisioning, Cox said. "And in the Oracle world, where a lot of the high-end systems are installed," he said, the popular database precludes the use of thin provisioning because it pre-formats the disk pools itself.

StorageIO Group's Schulz recommends factoring in the cost of monitoring tools when calculating the benefits of thin provisioning, and warns against creating performance bottlenecks by forcing too many servers to compete for read/write access to too few disks.

This was first published in September 2009

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