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Thin provisioning

Until recently, there wasn’t a real alternative to overprovisioning allocated storage and, as a result, storage utilization has been dismal. It’s not unusual for companies to have hundreds of gigabytes of overprovisioned and unused storage in their data centers. “Before we had Compellent arrays and thin provisioning, we relied on users helping us estimate storage requirements and we added 20% to 100% to user estimates, depending on what application it was for,” said Brandon Jackson, CIO of Gaston County, NC, describing the unscientific and wasteful process used by many organizations to ensure sufficient storage capacity.

Thin provisioning technologies can help put an end to this profligate management of storage resources by allowing storage to be assigned to users and servers beyond actual available physical capacity. Storage is allocated to thin-provisioned volumes on an as-needed basis. For instance, thin provisioning enables allocation of a 100 GB volume even though it may only have 10 GB of physical storage assigned. Thin provisioning is transparent to users, who will see a full 100 GB volume. The cost savings of thin provisioning can be tremendous and enables storage utilization beyond 90%.

The number of vendors that support thin provisioning is growing quickly, and it should be one of the key criteria when selecting a storage system. Keep in mind, though, that not all thin provisioning implementations are equal.

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While some systems require setting aside areas that can be thin provisioned, in others all capacity is available for thin provisioning without the need for special reservation. The ability to convert regular “thick” volumes into “thin” volumes, how unused storage is recovered and the way thin provisioning is licensed are other areas of differentiation. With more storage provisioned than physically present, running out of physical storage is an ever-present risk in thinly provisioned environments. Therefore, alerts, notifications and storage analytics are essential features that play an even greater role in thinly provisioned environments than they do in traditionally provisioned storage.

Efficient clones

Cloning is used to create an identical copy of an existing volume, and it has become more relevant with server virtualization where it’s frequently used to clone virtualized OS volumes. The most basic and still predominant implementation of a clone is creating a full copy of the source volume, with the cloned volume allocating the same amount of physical storage as the source volume.



The next level up is the ability to clone thinly provisioned volumes. While some storage systems turn thinly provisioned volumes into thick volumes during cloning, others can create a copy of a thinly provisioned volume where the thinly provisioned source volume and cloned volume allocate the same amount of physical storage. “In our Virtual Storage Platform [VSP], we’re able to create a thin-provisioned clone from another thin-provisioned volume,” said Mike Nalls, senior product marketing manager at Hitachi Data Systems’ enterprise platform division.

The most efficient clones are thin clones, where a cloned volume holds no data at all, but instead references blocks on the source image. Thin clones only have to store differences between the original image and the cloned image, resulting in huge disk space savings. In other words, a fresh clone requires minimal physical disk space and only as clones change do differences from the original image need to be stored. NetApp’s FlexClone and the cloning feature in the Oracle ZFS Storage Appliance (Sun ZFS Storage 7000 series) are examples of storage systems that support thin clones today.

This was first published in June 2011

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