STOR2RRD is a free and useful tools for SAN and storage performance and health monitoring. The tool is developed by XORUX. STOR2RRD supports wide range of SAN switches and SAN storage from most vendors.
The tool offers you end-to-end views of your storage environment including NAS and SAN and can save you significant money in operation monitoring and by predicting utilization bottlenecks in your virtualized environment.
You can also generate policy-based alerts, view overall health status of your systems, provide capacity reports and forecasting data.