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Get ready for virtualization

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Both Sadowski and Mikkelsen say this proxy capability appeals to users who want to gradually implement virtualization, but also want a quick exit if things go south. Even though the LUN is encapsulated by Invista or TagmaStore, neither product writes a signature nor any meta data on the LUN because it's now virtualized. However, TagmaStore's USP platform goes one step further and can simply re-present LUNs in their native format. A user could remove the USP platform from the server's data path and allow the host to directly access the LUNs on the storage array without having to migrate out of the virtualized environment.

Yet even when LUNs are in this most basic virtualized state, users still gain some of the benefits of virtualization. For instance, with EMC's Invista, they can non-disruptively migrate data to another device, such as moving data from a Symmetrix to a Clariion LUN. The new virtual Invista LUN has all of the characteristics a LUN presented by a storage array would have, such as the ability to set a SCSI-3 reservation bit that allows for clustering and to interoperate with their multipathing software. However, users who have heterogeneous server environments with a number of different multipathing software packages installed will want to consider storage vendors such as FalconStor and HDS, which support a wider variety of vendor multipathing software packages than EMC currently does.

Of course, back-out strategies work best when you're

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not too far down the virtualization path. When you begin implementing advanced virtualization features, such as storage volume management and asynchronous replication, the likelihood of lock-in becomes imminent. For instance, implementing a one-to-one mapping of a virtual LUN to an array LUN allows for an easy in and out of the virtualization solution. However, most users will want to take advantage of volume management features that enable LUN groups or meta-LUNs that concatenate or stripe data across volumes on the back end and allow the storage administrator to present five 20GB LUNs as one logical 100GB volume to a host. Once this type of feature is used, users abandon nearly any hope of finding an easy way out of a specific vendor's virtualization solution.

Running backups
The ramifications of backing up in a virtualized environment are also often overlooked. With all backups now running though a single interface, this is a likely spot for bottlenecks to appear. If users decide to use snapshots and asynchronous replication in lieu of or to complement backups, this will require a major restructuring of the way data is protected in the environment.

With the benefits of virtualization well known and the pain of managing SANs growing, this generation of network-based virtualization appliances delivers what the first generation of products didn't—interoperability, integration and the backing of major storage vendors. For enterprise shops, the decision about which virtualization appliance to deploy now depends less on the number of technical features it initially offers than on how stable it is, how easy it is to implement and how willing the vendor is to negotiate favorable terms. Yet with vendor lock-in likely, and the long-term control and management of enterprise data at stake, organizations should bring virtualization into their environments very cautiously.

This was first published in December 2005

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