StorPool implements 3-way or 2-way synchronous replication, meaning multiple full copies/replicas of the data exist.
With 3N the raw storage capacity is approximately 300% of the stored data capacity, not accounting for space saving features that reduce space usage and not including overhead that increases space usage.
For each data copy/replica there is 10% capacity overhead that includes checksums (for end-to-end data integrity), metadata and copy-on-write/thin provisioning overheads and safety. The capacity overheads are taken into account when performing StorPool sizing exercises. When a StorPool quote states a solution supports 100TB of stored data, it is really able to store 100TB of data.
StorPool, StorPool [SDS]/19.01, x86
Protection Capacity Overhead, Reads/Writes, Data Availability