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Thin provisioning risks vs. rewards

Thin provisioning is picking up steam in the storage industry; it seems like every manufacturer has the capability or something like it. But is it safe to offer to your customers?

As Alan

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Radding's article on SearchStorage.com attests, there's a fair amount of concern over whether thin provisioning is safe. Will the application run out of storage capacity before the customer can order more storage from you? While Alan has good guidelines to consider in the use of thin provisioning, the truth is that thinly provisioned storage is no more likely to run out of disk capacity suddenly than any other form of storage, for two reasons: It uses a global pool of storage, and before running out of space, there are tons of warnings.

Global pool of storage

With thin provisioning, free capacity is centralized into a global pool that all the thin volumes have easy access to. Instead of being preassigned to certain LUNs and volumes, the free space is available to any volume in the array. While there is risk of running out of capacity with thin-provisioned volumes -- Seiji Shintaku's recent article for SearchStorageChannel.com is a good illustration of the hassle that creates in a thinly provisioned replication system -- the global pool mitigates this risk and certainly simplifies volume expansion.

Low-space warnings

Beyond the peace of mind afforded by a global pool of storage, you and your customers should also rest easy knowing that before the global pool of a thinly provisioned system runs out of space, there are many warnings. In fact, to actually run out of space, you'd almost have to purposely ignore the warnings Most of these systems not only provide warnings when free space is low, they also can be customized to warn at different intervals so your customer has the time to work through their unique procurement process.

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Additionally, most thin-provisioned systems can also provide a trend report that will allow the customer to be proactive in their storage acquisitions. Armed with these reports, your customer can project months into the future and allocate storage accordingly. After about a week, you could consider the information in the trending report useful, though it will get more valuable over time, of course.

How to add value via thin provisioning

With these two big safety measures behind it, thin provisioning isn't going anywhere. If you've resisted learning how to use the technique, it's time to stop resisting and build some expertise around it since it's going to call for some special disciplines. For example, as we describe in our article "Converting from Fat Volumes to Thin Provisioning," there are challenges that occur when moving from a thick volume to a thin volume. It's important to know that migrating to and keeping thin volumes thin, while not complicated, requires a thorough understanding of the capabilities and, more importantly, the limits of the technology.

In addition to educating yourself on the ins and outs of thin provisioning, you should establish a best practices guide for your customers on topics such as how much capacity to overprovision on each volume, how to migrate to a thinly provisioned system, how to keep thinly provisioned volumes thin and the performance ramifications of a thinly provisioned volume. These guidelines will vary by vendor, so make sure you investigate each carefully.

Beyond a best practices guide for your customer, you can also add value by offering to monitor the thin-provisioning warnings and reports, most of which can be sent via email directly to you. Some customers will be happy to have you alert them when it's time to take action with their system rather than paying close attention to it themselves.

Here's Alan Radding's report on thin provisioning:

Best practices for effective thin provisioning

The major airlines are masters of thin provisioning; they just call it overbooking. Using the extensive data they have about every flight and its occupancy, they can pretty accurately predict how many passengers with reservations will be no-shows. So, they overbook. That we don't actually encounter overbooked flights all that often is a testament to how good their data and predictive algorithms are.

Thin provisioning is a form of overbooking. With thin provisioning, you provision a certain amount of storage capacity while actually allocating less disk capacity than you provisioned for. The application thinks it has a certain amount of capacity available to it, when it actually has less.

Read the rest of Alan Radding's report on thin provisioning.

About the author

George Crump is president and founder of Storage Switzerland, an IT analyst firm focused on the storage and virtualization segments. With 25 years of experience designing storage solutions for data centers across the United States, he has seen the birth of such technologies as RAID, NAS and SAN. Prior to founding Storage Switzerland, George was chief technology officer at one of the nation's largest storage integrators, where he was in charge of technology testing, integration and product selection. Find Storage Switzerland's disclosure statement here.

This was first published in July 2009

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