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Both Invista and SVC require new devices to be inserted into the data path. To install the devices, a storage admin needs to halt application processing, physically rearrange the cables of the FC SAN, and then change FC SAN zoning and storage system LUN masking settings to introduce the network-based virtualization software into the data path.
The absence of cache on EMC's Invista presents other longer term challenges. It will minimally delay, if not preclude, Invista from supporting features like asynchronous replication or thin provisioning because these technologies typically rely on cache to work. EMC plans to add thin provisioning to Invista in late 2008, but recommends users adopt its RecoverPoint product if they need to do asynchronous replication between different storage systems.
IBM's SVC more closely resembles a storage system controller because it uses cache in its architecture. The SVC storage virtualization code resides on Linux servers that are deployed in clustered configurations and mirror-write IOs over FC ports between the cache in the clustered pair. It supports four clustered pairs of servers in a logical configuration, with each clustered pair operating independently of the others.
Chris Saul, IBM's SVC marketing manager, recommends users first go through a capacity-planning exercise before implementing SVC. IBM is aware of congestion problems that can arise if users insert SVC into an existing FC SAN fabric and fail to isolate congestion-causing devices like tape from the SVCs. Sometimes the SVC is inserted in a core-to-edge design that puts excessive strain on inter-switch links (ISLs) which, says Saul, "increases the chances of ISL congestion."
Host-based approach
Storage managers often can't standardize on one or two vendors' storage; instead, they'll have to virtualize and manage the amalgamation of storage their company has accumulated over the years. In these types of cases, their best option is to select a storage virtualization product and SRM software that virtualizes and manages storage resources on the host.
For example, Symantec Corp.'s Veritas Storage Foundation provides a common way to virtualize a heterogeneous environment of storage system- or network-based storage virtualization products at the host. By using Veritas Storage Foundation, companies can virtualize and manage their storage in the same way across all of their platforms without needing to learn operating system-specific volume managers. Users can then manage the applications and storage devices using Symantec's Veritas CommandCentral Storage SRM software while gaining additional management benefits on hosts running Veritas Storage Foundation.
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