mapData utility does not copy buffer positions

Hi,

Somewhere in the guide it is mentioned that mapData can not copy buffer positions. What does it mean by buffer positions?

Also we were using mapData to copy the entire source domain data to the destination domain. We did map data for the global domain as well as for all the local domains. mapData completed successfully without any issue but the size of the destination domain is much much smaller than the source domain. What is missed? Is it buffer positions which are not copied? and what is the impact further?

Thanks,

S.Heda