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Ask the expert: When to use thin provisioning

What’s thin provisioning and should I use it for my virtual servers?

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Helmick: Should you use thin provisioning for your virtual servers? Yes, you should!

Thin provisioning allows you to allocate future disk storage space for a virtual disk without demanding storage space immediately. Rather than creating a fixed file size (fat provisioning), a small file grows on demand until it reaches a predetermined maximum size. In Microsoft Hyper-V, this is referred to as dynamic disks, but that concept is essentially the same as VMware vSphere thin provisioning.

The benefits to thin provisioning virtual disks for your virtual servers are enormous. Thin provisioning conserves physical disk space until it’s needed. Virtual server and disk migrations are faster because only the amount of disk space needed is in use -- not the maximum allocated size. Space-saving practices, such as deduplication and archiving, keep virtual disk sizes low, leaving unallocated physical space for more virtual disks and servers. This maximizes your investment in your storage device by only using the disk space necessary.

There are some drawbacks to thin provisioning. However, most can be avoided with good monitoring practices. The most common snag is overprovisioning a storage platform. This happens when the total maximum allocated size of all virtual disks exceeds the physical storage capabilities of your host’s storage device.

Careful monitoring of disk space usage will alert you when to add physical storage or practice disk-space saving measures. This might affect performance on larger virtual servers requiring rapid data growth. Microsoft and VMware have optimized the performance of thin provisioning so that, in most situations, isn’t an issue. However, it’s worth checking with your storage vendor’s recommendations.

For the most part, thin provisioning decreases wasted disk space while permitting an increase in virtual disk density. With good planning and monitoring, you will avoid the pitfalls of overprovisioning and maximize the investment in your storage devices.

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This was first published in November 2012

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