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The most acute problem virtualization creates in heterogeneous storage networks is the inability to map exactly what application data resides on which specific disk. As each layer of virtualization further abstracts the data from the underlying disk to simplify management, information such as storage system RAID levels or controller configurations (needed to optimize performance and troubleshoot problems) is lost. Accessing this information and mapping it back to the application almost always requires access to the storage systems' APIs.
These problems have led EMC and IBM to develop their respective ControlCenter and TotalStorage Productivity Center (TPC) SRM software suites to integrate most tightly with their own hardware and software products. While the EMC and IBM SRM software supports SMI-S and APIs from other storage systems, Rymarczyk admits that "customers will lose some of their freedom to pick other vendors' storage" if they use IBM's SRM software.
EMC and IBM took significantly different approaches to the architectures of their network-based storage virtualization products. EMC's Invista is a split-path architecture that places the storage virtualization code on a management or control path workstation that resides outside of the FC SAN. Virtualization settings are configured on the control path workstation, which then uploads the code into a cache-less FC switch called the
| data path controller, such as Brocade's AP7420, or a director blade like the Cisco Systems Inc. MDS 9000 Family Storage Services Module (SSM).
Doc D'Errico, VP and general manager of EMC's infrastructure software group, says this "stateless" approach preserves the intelligence on storage systems because storage systems perform other tasks such as replication and data optimization. If all of the intelligence was removed from the storage system and placed on an appliance, users would lose some of the inherent benefits provided by storage systems. Keeping the intelligence on the storage systems also prevents users from making a long-term commitment to network-based virtualization. "Users can transition in and out of network-based virtualization more easily using Invista," claims EMC's D'Errico.
The new 2.0 release of Invista addresses some of the deficiencies of the first release. In the first release, the lack of physical redundancy in its Control Path workstations was considered a potential liability. Invista 2.0 creates a Control Path Cluster (CPC) that's physically separated by FC distances; so if CPC workstation 1 fails, CPC workstation 2 can take over. Invista 2.0 also takes advantage of PowerPath's load-balancing features so it can dynamically load balance between the data path controller and back-end storage systems.
This was first published in January 2008