Este PDF parece ter uma explicação disso, junto com novos recursos do NTFS.
Diz:
Slab Consolidation
Efficiently defrags files to minimize the number of allocated slabs
A slab is the unit of allocation on a thin provisioned volume
Requires support for
IOCTL_STORAGE_QUERY_PROPERTYrequesting a property ID of:StorageDeviceLBProvisioningProperty
- Retrieves a volume's slab size