10.2 Storage Resource Management

In the SAN management hierarchy, storage resource management (SRM) applications are a subset of more comprehensive storage management platforms. SRM applications are available as stand-alone programs or as plug-in modules for broader management applications. They are written to either homogeneous or heterogeneous operating system environments.

The primary value offered by these programs is the ability to make all distributed disk assets visible to a single management console. Because SRM applications are focused exclusively on storage availability and utilization, the way that storage is physically connected to servers is largely transparent. Therefore, SRM applications are not unique to SANs but may also encompass internal workstation-attached, SCSI-attached, and NAS storage. The SAN-specific features of a storage resource application surface when, via the SAN interconnection, multiple servers have access to the same storage arrays and when the SRM workstation itself is SAN-attached.

Without a storage resource mechanism, disk administration is limited to individual servers. For an enterprise with hundreds or thousands of servers, and consequently hundreds or thousands of disks and arrays, it would be overwhelming to manually consolidate information on disk utilization, location of operating systems, location of common applications, the amount of disk space budgeted for users or departments, and so on. Consequently, applications are unnecessarily duplicated on multiple servers, and disk space is underutilized in some departments and overutilized in others. In addition, tape backup requirements cannot be properly sized, and sudden outages due to disk starvation cannot be anticipated.

Storage resource management addresses these shortcomings by automating the process of disk information retrieval and presenting a single view of all disk resources. SRM client software on each server periodically updates information on its assigned volumes and directories and forwards this data to the SRM manager. The SRM management platform, in turn, consolidates the status information from multiple clients in a relational database and may, depending on the vendor's implementation, provide storage policies that issue alerts when usage thresholds are exceeded. As with trending tools in local and wide area networks, SRM applications may also offer enhanced capacity planning utilities that facilitate redistribution of storage resources and provide data for accurate budget forecasts of impending storage needs.

Because SANs enable a storage-centric model, SRM applications can be leveraged more effectively for optimal use of storage than can fixed SCSI configurations. JBODs and RAIDs on a storage network, for example, offer more flexibility in redistribution of disk space between SAN-attached servers and more easily accommodate increases in the pool of storage without system down time. At a higher level, storage utilization data via SRM can be correlated with transport utilization via storage network management to determine the optimum configuration of servers and storage to meet capacity requirements and traffic patterns.