Storage Virtualization: What's the Alternative?

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In-band storage-virtualization software, where both metadata and storage run on a shared data path, may be the most widely deployed method today, but there are many other alternatives that are gaining traction.

A more scalable option is virtualization software based on a split-path architecture, whereby the data and the management and routing information run separately and the software runs on, or is associated with, a SAN switch. Among those offering virtualization software based on the split-data path are EMC, with its InVista software, and Incipient, a relative newcomer that just last month started shipping its Network Storage Platform (NSP). Both run within Cisco MDS 9000 switches.

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EMC's InVista is primarily targeted at EMC Symmetrix shops. Observers say few customers have deployed InVista, and EMC hasn't targeted the solution to its indirect channel.

Incipient says NSP offers a more vendor-neutral approach, although it currently must run in Cisco's MDS SAN switches. NSP is embedded within storage blades that run on the MDS 9000 switch.

Like EMC's InVista, Incipient's NSP is currently suited for large organizations, such as banks and telecom carriers that need to scale into the petabytes.

"These big accounts and service providers aren't willing to put an appliance in the data path," says Robert Infantino, Incipient's senior vice president of marketing and alliances. "It's not going to scale."

That may be true in some cases, but there's a huge number of shops that don't need that level of scalability. Typical IBM SVC implementations virtualize, on the average, 50 TB to 70 TB, although IBM says it has customers with up to 500 TB of storage supported by SVC.

As it stands now, the split-data path architectures on the scale of EMC's InVista and Incipient's NSP are yet to be proven.

Another vendor whose virtualization software runs with specific SAN switches is StoreAge Networking Technologies, which was recently acquired by LSI Logic, although it runs on midrange switches from QLogic, McData and Emulex. With its 500 installations of SAN Virtualization Manager, the concept needs no validation, says Kevin Liebel, LSI's marketing director. "The split-path architecture is much better for the long term," Liebel says.

Another option is array-based virtualization. Hitachi Data Systems, whose TagmaStore is sold under the HDS brand, and under license by HP and Sun, offers connectivity to a significant variety of competitive storage offerings. Critics are quick to point out that this controller-based solution is geared toward locking customers into the TagmaStore platform, but that it has strong connectivity and app support.

Other hardware-agnostic options include Symantec's newly released Veritas Storage Foundation 5.0 High Availability. With a new version that supports Windows, Linux and Unix, the company has combined its Veritas Server Cluster software with its Storage Foundation. The result is data-migration software that the company argues is far less complex than TagmaStore or Invista. For example, the Veritas Storage Foundation supports integration with VMware's ESX 3.0, which enables fail-over and monitoring of apps across physical and virtual machines

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