The storage devices of a storage device set (e.g., a RAID array) may generate a nonvolatile representation of the configuration of the storage device set, including logical disks, spaces, storage pools, and layout and provisioning plans, on the physical media of the storage devices. A computer accessing the storage device set may also generate a volatile memory representation of the storage device set to use while accessing the storage devices; however, the nonvolatile representation may not be performant due to its different usage and characteristics. Presented herein are techniques for accessing the storage device set according to a volatile memory representation comprising a hierarchy of logical disks, slabs, and extents, and an accessory comprising a provisioning component that handles slab accesses while applying provisioning plans, and that interfaces with a lower-level layout component that translates slab accesses into storage device accesses while applying layout plans to the storage device set.