The Free On-line Dictionary of Computing (30 December 2018):

New Storage System

    (NSS) A major Multics implementation project
   during the 1970s.  The initial Multics file system design
   had evolved from the one-huge-disk world of CTSS.  When
   multiple disk units were used they were just assigned
   increasing ranges of disk addresses, so a segment could have
   pages scattered over all disks on the system.  This provided
   good I/O parallelism but made crash recovery expensive.
   NSS redesigned the lower levels of the file system,
   introducing the concepts of logical volume and physical
   volume and a mapping from a Multics directory branch to a
   VTOC entry for each file.  The new system had much better
   recovery performance in exchange for a small space and
   performance cost.

   (1997-01-29)