You are copying files or folders onto a USB or Removable Storage Device and you find that it takes an excessive amount of time.
Policies which include compound exceptions, two-tier detection (see TECH220967), or regular expressions can require more time than a simple keyword policy in detection on the Endpoint Agent system. In some cases latency will depend on your system CPU, Memory and USB speed e.g. 1.0 or 3.0. To determine the exact cause of the excessive latency you will need to do some initial investigation.
To investigate this issue break it into two areas (i) Resources and (ii) Policies then check the following:
For assistance on policy tuning please refer to the chapter entitled "Best practices for authoring policies" in the Symantec Data Loss Prevention Administration Guide.
For guidance on expected latency while copying data to USB/Removable Storage devices please consult the Symantec Data Loss Prevention Endpoint Performance Guide, specifically the chapter entitled "Latency testing".