(S2D) Mirroring

Storage Spaces Direct (S2D) Block-Level Mirroring

• The actual data mirroring in S2D is handled at the block level, within the S2D storage pool itself, not at the file system or network protocol level.
• S2D implements data resiliency through various types of storage layouts, including:
  • Mirroring: This mirrors the data between two or more physical drives (usually across multiple nodes in the cluster).
  • Parity: This is a more space-efficient method than mirroring, but it uses parity data to reconstruct lost data instead of duplicating it.
• The block-level protocols involved here include:
  • SCSI (Small Computer System Interface): SCSI commands are used for storage operations like read and write.
  • iSCSI or SMB3 (in some scenarios): These are used to expose the storage (such as CSVs) over the network for access by clients, but not for mirroring itself.

Storage Cluster Communication (CSAPI)

• Internally, Storage Spaces Direct (S2D) uses Cluster Storage API (CSAPI) to manage communication and replication between cluster nodes for data mirroring.
• CSAPI facilitates the distributed storage management, ensuring that data is mirrored and synchronized between different nodes in the cluster.
• This communication occurs over TCP/IP networks, but the actual mirroring and replication operations happen using block-level protocols like SCSI.