NVMe/TCP MultiPath

NVMe multipath I/O refers to two or more independent paths between a single host and a namespace. Each path uses its controller, although multiple controllers can share a subsystem port. Multipath I/O like namespace sharing requires that the NVMe subsystem contains two or more controllers.

Multipath is part of NVMe specification and is used by the Lightbits cluster software as follows:

1. The primary node exposes the path to the volume.
2. Clients send read and write requests to the primary node.
3. The primary node replicates to the secondary nodes.
4. If the primary node fails, the secondary node exposes a path to the client so the client can continue working with the secondary node.

Lightbits uses a proprietary protocol on top of TCP to replicate data between primary and secondary nodes, without requiring any changes to the client.