In my c# Windows Forms application (.net 3.5 / VS 2008) I have 3 settings files resulting in one user.config file.

One setting file consists of larger data, but is rarely changed. The frequently changed data are very few. However, since the saving of the settings is always writing the whole (XML) file it is always "slow".

SettingsSmall.Default.Save(); // slow, even if SettingsSmall consists of little data 

Could I configure the settings somehow to result in two files, resulting in:

SettingsSmall.Default.Save(); // should be fast
SettingsBig.Default.Save(); // could be slow, is seldom saved

I have seen that I can use the SecionInformation class for further customizing, however what would be the easiest approach for me? Is this possible by just changing the app.config (config.sections)?

--- added information about App.config

The reason why I get one file might be the configSections in the App.config. This is how it looks:

  <configSections>
    <sectionGroup name="userSettings" type="System.Configuration.UserSettingsGroup, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
      <section name="XY.A.Properties.Settings2Class" type="System.Configuration.ClientSettingsSection, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" allowExeDefinition="MachineToLocalUser" requirePermission="false" />
      <section name="XY.A.Properties.Settings3Class" type="System.Configuration.ClientSettingsSection, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" allowExeDefinition="MachineToLocalUser" requirePermission="false" />
    </sectionGroup>
  </configSections>

I got the sections when I've added the 2nd and 3rd settings file. I have not paid any attention to this, so it was somehow the default of VS 2008. The single user.config has these 3 sections, it is absolutely transparent.

Only I do not know how to tell the App.config to create three independent files instead of one. I have "played around" with the app.config above, but e.g. when I remove the config sections my applications terminates with an exception.