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Storage virtualization: It’s ready, are you?

Ezine

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Adoption of storage virtualization has been accelerating as some of the early obstacles to implementation have fallen by the wayside. There’s a wide choice of mature products whether you decide to deploy storage virtualization at the array or in the network.

While there may be some dispute over an exact definition, storage virtualization is generally considered technology that provides a flexible, logical arrangement of data storage capacity to users while abstracting the physical location from them. It’s a software layer that intercepts I/O requests to the logical capacity and maps them to the correct physical locations.

The most basic implementation of storage virtualization is at the host level, where a logical volume manager allows the simple provisioning of storage capacity to apps and users. While also implemented with file storage systems, block storage virtualization is more commonly implemented due to the complexity of LUN management and the requirements for flexibility in storage provisioning, especially in multi-user environments. This article covers storage virtualization technologies at the network and storage device level, not at the host level.

Goodbye to groups, LUNs and partitioning

The legacy process of creating array groups, allocating LUNs and partitioning volumes is a complicated and inefficient way to provision storage, particularly when it involves balancing performance and reliability

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of physical disks across drive shelves. Similarly, expanding an existing host’s volume can be a time-consuming process of concatenating LUNs and copying data. Storage virtualization provides a better way to keep up with the demands of provisioning storage to applications and servers while reducing time and resources expended by allowing the “brains” of the storage system to make most of the decisions. It can also improve utilization by replacing the guesswork of manual allocation while supporting technologies like thin provisioning.

Initially, virtualization was simply a tool used to provision and manage storage efficiently. But by isolating the host from physical storage, the technology also enabled storage capacity in different physical chassis (even from different manufacturers) to be logically combined into common pools that could be managed more easily. While some of these heterogeneous systems were used to create larger volumes than were physically present on any one disk array, most use cases employed storage virtualization as a common management platform. This enabled existing storage systems to be repurposed and reduced the overhead associated with managing multiple silos of storage, although the physical disk systems still needed to be maintained.

Virtualization can improve performance as host volumes are easily spread across larger numbers of disk drives, which could negatively affect capacity utilization. Virtualization also allows storage tiering and data migrations between devices, such as moving older data to an archiving appliance or hot database indexes to a solid-state drive (SSD) cache. These activities are typically carried out based on policies set at the host, application or file level, and the same data movement mechanism can be used to migrate data offsite for disaster recovery (DR) purposes.

This was first published in August 2011

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