Raid-S is a proprietary version of RAID (Redundant Array of Inexpensive Disks) developed and used by the EMC Corporation (now owned by Dell and known as Dell EMC) for use in a enterprise SAN (storage area network) storage array solution known in the Symmetrix (Where the "S" comes from). Raid-S was only available in the early 2000's within this Dell EMC Product and has been deprecated as RAID 1,10,5,6 provided more practical in later models.
This concept of RAID is similar to other more common (and capable) RAID methods (RAID-1/0, RAID-5, RAID-6), as it protects against data loss (of active data) when a disk fails.
To better understand RAID-S, we first have to understand RAID-3 (another uncommon raid, that was used before RAID 5/6 took over the parity RAID space). RAID-3 is similar to RAID-5 as it uses parity based protection and can tolerate 1 disk failure. The big difference between the two is that RAID-5 distributes the parity data across all involved disks (in the RAID set), while RAID-3 only holds the parity on a single disk dedicated to the task. RAID-3 does allow any of the disks to fail (including the Parity Disk), as RAID-5 does, however, the speed of the array is limited to the speed of the parity drive. RAID-5 doesn't suffer this limitation (hence why nobody uses RAID-3 anymore either).
Now RAID-S is almost the same as RAID-3, except the non-parity drives (the data drives), are not participating in a single RAID Set (Volume / Pool / Filesystem), but each member is typically part or all of its own filesystem. This context is where RAID-S makes sense.. In a large storage subsystem (Symmetrix) that is providing multiple volumes (similar sized LUNs over Fiber Channel SAN technology) to multiple external servers. RAID-S protects these multiple volumes (within a single Symmetrix system) by allowing a parity volume to be allocated to a set of these server volumes, thus protecting all associated volumes by parity.
This technology (RAID-S) lives on today (in a prosumer / SBS product) called UNRAID. UNRAID is similar in nature where each disk have it's own filesystem, however one or two dedicated parity drives are allocated to protect the various filesystems on the associated disks. This product is more geared towards the cold / warm data storage market (NAS / backup), while RAID-S was geared (by where it was implemented) towards the hot data storage market (providing storage to active servers in a datacenter).