Amazon Neptune storage, reliability and availability
Amazon Neptune uses a distributed and shared storage architecture that scales automatically as your database storage needs grow.
Neptune data is stored in a cluster volume, which is a single, virtual volume that uses Non-Volatile Memory Express (NVMe) SSD-based drives. A cluster volume can grow to a maximum size of 128 tebibytes (TiB) (64 TiB in the China Regions and the AWS GovCloud (US) Regions). A cluster volume consists of copies of the data across three Availability Zones (AZs) in a single AWS Region, which provides high durability and availability.
The Storage section covers these topics in detail:
Allocation – You are charged for space allocated, as determined by the storage high water mark.
Storage billing – Storage costs are billed based on the high water mark, and Neptune also offers an I/O–Optimized pricing option for I/O–intensive workloads.
Reliability and high availability – Neptune replicates your data across three Availability Zones for high durability and automatic fault recovery.