Use external commands to get and set quotas?
When this option is set to Yes, Virtualmin will use the commands in
the configuration options below it to set and get user and group quotas. This
can be useful if quotas on your server are managed in some way other than the
standard Unix quota system, such as by a NFS server or ZFS filesystem.
By default it is set to No, which is the correct setting for almost
all systems.