Manual:$wgUploadThumbnailRenderMap/fr

Détails
S'il est défini, c'est un tableau de largeurs de vignettes générées au moment du téléversement. The idea is to prerender common thumbnail sizes, in order to avoid the necessity to render them on demand, which has a performance impact for the first client to view a certain size.

This obviously means that more disk space is needed per upload upfront.