Monitoring disk I/O

There are several issues you should consider to determine your course of action when you are monitoring disk I/O.

  • Find the most active files, file systems, and logical volumes:
    • Can "hot" file systems be better located on the physical drive or be spread across multiple physical drives? (lslv, iostat, filemon)
    • Are "hot" files local or remote? (filemon)
    • Does paging space dominate disk utilization? (vmstat, filemon)
    • Is there enough memory to cache the file pages being used by running processes? (vmstat, svmon)
    • Does the application perform a lot of synchronous (non-cached) file I/O?
  • Determine file fragmentation:
    • Are "hot" files heavily fragmented? (fileplace)
  • Find the physical volume with the highest utilization:
    • Is the type of drive or I/O adapter causing a bottleneck? (iostat, filemon)

Construction of a pre-tuning baseline

Before you make significant changes in your disk configuration or tuning parameters, it is a good idea to build a baseline of measurements that record the current configuration and performance.