Extra command-line parameters for compression command
By default, Virtualmin runs the gzip or bzip2 commands
for compressing backups with no additional parameters. This means that the
default compression level and format will be used. However, you can use this
field to enter additional parameters, such as --fast to make your
backups run faster (at the cost of requiring more space), --best to get
better compression (at the cost of CPU time), or --rsyncable to make the
file more easily replicatable.