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Thin provisioning can help you use your disk capacity much more efficiently, but you need to get under the hood a little to understand how thin provisioning will work in your environment.

Nobody wants to pay for something they're not using, but enterprise data storage managers do it all the time. The inflexible nature of disk storage purchasing and provisioning leads to shockingly low levels of capacity utilization. Improving the efficiency of storage has been a persistent theme of the industry and a goal for most storage professionals for a decade, but only thin provisioning technology has delivered tangible, real-world benefits.

The concept of thin provisioning may be simple to comprehend, but it's a complex technology to implement effectively. If an array only allocates storage capacity that contains data, it can store far more data than one that allocates all remaining (and unnecessary) "white space." But storage arrays are quite a few steps removed from the applications that store and use data, and no standard communication mechanism gives them insight into which data is or isn't being used.

Storage vendors have taken a wide variety of approaches to address this issue, but the most effective mechanisms are difficult to implement in existing storage arrays. That's why next-generation storage systems, often from smaller companies, have included effective thin provisioning technology for some time, while industry stalwarts may only now

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be adding this capability.

What you should ask about thin provisioning

When evaluating a storage array that includes thin provisioning, consider the following questions, which reflect the broad spectrum of approaches to this challenge. Note that not all capabilities are required in all situations.

  • Is thin provisioning included in the purchase price or is it an extra-cost option?
  • Does the array support zero page reclaim? How often does the reclamation process run?
  • What is the page size or thin provisioning increment?
  • Does thin provisioning work in concert with snapshots, mirroring and replication? Is thick-to-thin replication supported?
  • What does the array do when it entirely fills up? What's the process of alerting, freeing capacity and halting writes?
  • Does the array support WRITE_SAME? What about SCSI UNMAP or ATA TRIM?
  • Is there a VMware vStorage APIs for Array Integration (VAAI) "block zeroing" plug-in? Is it the basic T10 plug-in or a specialized one for this array family?
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This was first published in April 2011

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