Detail Considerations

1.

degree of detail desired Determines how much uncertainty is minimized. It would be best to measure and test the real system; however one approach toward uncertainty minimization is the following. [TWL94]

• Use real file system code as file system simulator. [TWL94]
• Use real traces rather than synthetic ones. [TWL94]
• Calibrate disk system against real disks. [TWL94]

2.

degree of detail required Very important for getting useful results. For example, ignoring caching effects, which depend on rotation position in the disk, can result in mean simulated times as much as a factor of two larger. [TWL94]

3.

cost of detailed models As processors speed up relative to I/O, a disparity in performance increases. It becomes possible for the elapsed time for executing the simulations to be much less than the time required to execute the real system executing the traced workload. [TWL94]

Since omitting crucial details can be dangerous, the authors believe that the accuracy and confidence in results gained by building scaffolding and constructing a detailed model is well worth the extra time required. [TWL94]