Method and device for writing multiple-layer optical discs

A method of writing information in a storage layer (2A,2B) of a multi-layer optical storage medium (2) comprising two or more storage layers (2A,2B), especially multi-layer recordable and rewritable optical discs, especially DVD discs or BD discs. The method comprises the steps of monitoring a focus condition of an optical write beam (32b), and inhibiting the writing process in case of an axial focus displacement event. Also described is a medium access device (10), capable of writing information in a storage layer (2A,2B) of a multi-layer optical storage medium (2). The medium access device (10) comprises: light beam generating means (31) for generating a write light beam (32); focussing means (34) for focussing the write (32) in a focal spot (F) at a target storage layer (2A); write inhibit means (64) for inhibiting a writing process in case of an axial focus displacement event.