To monitor volume performance in a clustered Data ONTAP 8.3 environment, OnCommand Performance Manager and Quality of Service (QoS) commands would be the most effective tools. OnCommand Performance Manager provides comprehensive performance monitoring, analysis, and reporting specifically for clustered Data ONTAP systems. Quality of Service commands allow you to monitor and control the performance of workloads by setting performance thresholds and handling performance statistics on a granular level. OnCommand System Manager is more for system configuration and management, and Syslog Server is primarily used for collecting and storing log messages but not specifically for detailed volume performance monitoring.