SCSI Physical Drive Functional Test 1. This is a percentage value that represents the operating efficiency of a drive. The functional test issues a series of SCSI commands and times the results. When the drive has the test run for the very first time (service time is zero), the results are saved as the baseline value. Then, whenever the test is executed the current result is compared to the baseline result and expressed as a percent. If the percentage result should drop rapidly there may be a problem with the drive. You may wish to replace the drive as a precaution.