Upgrading software on a cluster of computerized devices

A computerized device, comprising:

• a network interface constructed and arranged to provide external access to the computerized device, wherein the computerized device is a computerized node of a cluster which operates as a clustered storage system, each computerized node of the cluster being constructed and arranged to receive input/output (I/O) requests from a set of external host devices and perform I/O operations based on the I/O requests;
• memory which initially stores a first package of software;
• and
• processing circuitry coupled to the network interface and the memory, the processing circuitry being constructed and arranged to:
• run the first package of the software,
• during an installation period and after running the first package of the software for a period of time, receive a second package of the software through the network interface and install the second package of the software in the memory in place of the first package of the software, the second package of the software including a first version side and a second version side, the second package of the software further including a multiplexing stage which is constructed and arranged to steer I/O operations to either the first version side or the second version side,
• after the installation period and prior to running the second version side of the second package of the software, receive a group steering command by the multiplexing stage of the second package of the software installed on that computerized node,
• in response to the group steering command and completing processing of I/O requests started before receipt of the group steering command, steer, via the multiplexing stage of the second package of the software, (i) subsequent I/O requests received from a first group of external host devices only to the first version side of the second package of the software on that computerized node and (ii) subsequent I/O requests received from a second group of external host devices only to the second version side of the second package of the software on that computerized node, the first and second groups being non-overlapping, and
• after the installation period, run the second version side of the second package of the software.

A method of upgrading software running on a cluster of computerized nodes, the method comprising:

• running a first package of the software on each computerized node of the cluster, wherein the cluster of computerized nodes is a clustered storage system, each computerized node of the cluster being constructed and arranged to receive input/output (I/O) requests from a set of external host devices and perform I/O operations based on the I/O requests;
• during an installation period and after running the first package of the software on each computerized node of the cluster for a period of time, installing a second package of the software on each computerized node of the cluster in place of the first package of the software, the second package of the software installed on each computerized node of the cluster including a first version side, a second version side, and a multiplexing stage for steering I/O operations which are directed to the multiplexing stage to either the first version side or the second version side of the second package of the software installed on that computerized node, at least one computerized node of the cluster running (i) the first package of the software or (ii) the first version side of the second package of the software at all times during the installation period;
• after the installation period and prior to running the second version side of the second package of the software on each computerized node of the cluster, receiving a group steering command by the multiplexing stage of the second package of the software installed on that computerized node,
• in response to the group steering command, steering, by the multiplexing stage of the second package of the software installed on that computerized node, (i) all subsequent I/O requests received from a first group of external host devices only to the first version side of the second package of the software on that computerized node and (ii) all subsequent I/O requests received from a second group of external host devices only to the second version side of the second package of the software on that computerized node, the first and second groups being non-overlapping, and
• after the installation period, running the second version side of the second package of the software on each computerized node of the cluster.