Chapter 7. Highly Available controller pairs 71 Nondisruptive hardware maintenance: When you halt one node and allow takeover, thepartner node continues to serve data for the halted node. You can then replace or repairhardware in the node you halted.Figure 7-2 shows an HA pair where Controller A has failed and Controller B took overservices from the failing node.Figure 7-2 Failover configuration7.1.2 Characteristics of nodes in an HA pairTo configure and manage nodes in an HA pair, you need to know the characteristics that alltypes of HA pairs have in common: HA pairs are connected to each other. This connection cen be through an HA interconnectthat consists of adapters and cable, or, in systems with two controllers in the samechassis, through an internal interconnect. The nodes use the interconnect to do thefollowing tasks:– Continually check whether the other node is functioning.– Mirror log data for each other’s NVRAM.– Synchronize each other’s time. They use two or more disk shelf loops, or third-party storage, in which the followingconditions apply:– Each node manages its own disks or array LUNs.– Each node in takeover mode manages the disks or array LUNs of its partner. Forthird-party storage, the partner node takes over read/write access to the array LUNsowned by the failed node until the failed node becomes available again.its
