Video Library does not work

[kiney]

I played a little with the cache settings in guisetting.xml, but I don't really get it.
Is the file documented somewhere?
Theres an option

Code:

<cache>
        <harddisk>256</harddisk>
</cache>

That seems to have no effect at all on videos. And another section

Code:

<cachevideo>
        <dvdrom>2048</dvdrom>
        <internet>4096</internet>
        <lan>2048</lan>
    </cachevideo>

Where there is no option for harddisk. If I add a <harddisk> tag on my own, xbmc removes it on next startup.
Also where is the difference of these caches to <cachemembuffersize> in advancedsettings.xml?