MirrorPeriod defines the period of time
when indexer is allowed to reuse previously mirrored
instead of real downloading (to reduce Internet traffic).
Using mirrors as crawler cache can be useful
when you are doing experiments with mnoGoSearch to find the best configuration
that suites your need.
The default value of is -1,
which means that the mirrored files are not used
as crawler cache.
See the Period command description
for time format.