Data resynchronization

A non-transitory computer-readable storage medium comprising instructions that, when executed by one or more processors, cause the one or more processors to re-synchronize data between a first data storage volume and a second data storage volume, wherein the instructions are executable to:

• communicate data to the second data storage volume, from a start point to an end point of the first data storage volume;
• maintain a first cursor to indicate how much of the data has been communicated to and committed to persistent storage of the second data storage volume;
• and
• maintain, based on said communication, a second cursor to indicate how much data has been communicated to and buffered without yet being confirmed as committed to persistent storage of the second data storage volume.

A storage apparatus to re-synchronize data in a downstream volume thereof with data from a system storing an upstream volume, comprising:

• a first data buffer to receive given data that is to re-synchronize certain data in persistent storage of the downstream volume with the upstream volume;
• a second data buffer to receive, after receipt of the given data into the first data buffer, new data that is to overwrite the certain data in the persistent storage of the downstream volume;
• and
• a processor to execute stored instructions to commit to persistent storage of a current version of the downstream volume the new data in the second data buffer, after the given data in the first data buffer has been committed to persistent storage of the current version of the downstream volume, and to communicate an acknowledgement message to the system storing the upstream volume, the message indicating how much data has been committed to persistent storage of the current version of the downstream volume.