Most of the space was occupied by a few large files. This has the effect of loading the filesystem cache with as much data as it will hold. Otherwise, this might be done on the first test pass, artificially lengthening its run time in comparison with subsequent passes. The null device on the local hosts. Tape drive on the local host, by way of the variable block driver.
Remote tape drive via ethernet.
The same series of tests were repeated. We can then calculate the fixed overhead involved in setup and cleanup, by taking the total time for the larger filesystem, minus the size of the filesystem multiplied by the differential data rate. If output is to a tape device, it includes tape positioning, startup and rewinding time. This reflects the relatively slow performance of 8mm drives for rewinding, writing filemarks, and other bookkeeping operations. The high level of consistency of overhead calcualtions affirms the general validity of the test results and methodology.