Performing mirroring of a logical storage unit

An article comprising at least one computer-readable storage medium containing instructions that when executed cause a first storage controller to:

• receive write requests to perform writes to a logical storage unit;
• in response to the write requests, creating a first log segment containing entries for the write requests;
• transmit information from the entries of the first log segment to a mirror system to replicate the writes to a mirror copy of the logical storage unit;
• receive at least one command to transfer control of the logical storage unit from the first storage controller to a second, different storage controller;
• in response to the at least one command to transfer control of the logical storage unit, add a marker to the first log segment;
• and
• transmit the marker from the first log segment to the mirror system to allow the mirror system to synchronize replication of writes to the mirror copy of the logical storage unit performed by multiple storage controllers.

A storage subsystem comprising:

• a cluster of storage controllers;
• and
• a pool of storage resources accessible by the storage controllers, wherein at least one logical storage unit is defined on the pool of storage resources,
• the storage controllers to maintain corresponding log segments containing entries for writes performed to the logical storage unit performed by respective storage controllers,
• wherein at least some of the log segments contain markers to be communicated by corresponding storage controllers to a remote mirror system to enable the remote mirror system to replicate writes corresponding to the at least some log segments in original order of the writes.