text: **Note:**Comprestimator can run for a long period (a few hours) when it is scanning a 
  relatively empty device. The utility randomly selects and reads 256 KB samples from the 
  device. If the sample is empty (that is, full of null values), it is skipped. A minimum number 
  of samples with data is required to provide an accurate estimation. When a device is 
  mostly empty, many random samples are empty. As a result, the utility runs for a longer 
  time as it tries to gather enough non-empty samples that are required for an accurate 
  estimate. The scan is stopped if the number of empty samples is over 95%. 