Taking a consistent cut during replication for storage across multiple nodes without blocking input/output

Abstract

A replication appliance maintains dependent-write consistency on replicated storage, for write operations made by multiple nodes to a primary storage destination, without blocking storage I/O operations. The replication appliance transmits a notification to each node, indicating to check a centralized location for a token prior to each I/O operation. The replication appliance atomically generates the token, and the nodes detect it prior to executing corresponding I/O operations. In response to detecting the token, each detecting node inserts a consistency marker in its I/O stream, proceeds with the corresponding I/O operation, and stops checking for the token. The appliance reads the I/O stream of each node, and identifies the position of the inserted consistency marker. Using the identified positions in the I/O streams, the appliance creates a consistent cut without blocking I/O operations made by the nodes. The appliance uses the cut to maintain dependent-write consistency to the replicated storage.