A tracking layer in your map uses the Refer to data on disk (no separate copy) storage policy. This may cause poor drawing performance.
Analyze the drawing performance of your tracking layer in the Preview ArcGIS Server window. If the performance is unacceptable, change the Storage Policy of the tracking layer to Copy all data to memory on the Time tab of the Layer Properties dialog box, then reevaluate the drawing performance. For convenience, this tab can also be opened by right-clicking on the warning message and selecting Change Layer Time Properties.
In most cases, it is best to use the Copy all data to memory storage policy. Copying data to memory makes the tracking layer display faster. The only benefit to using the Refer to data on disk (no separate copy) storage policy is that larger datasets can be loaded into a tracking layer. Therefore, it is only appropriate when you are working with a tracking layer that is using a very large dataset. In that case, of course, you may also experience poor performance due to the size of the dataset. Therefore, you will need to experiment to find the best settings for your data.