Characteristics Of Nodes In An Ha Pair - IBM N Series Hardware Manual

Nondisruptive hardware maintenance: When you halt one node and allow takeover, the
partner node continues to serve data for the halted node. You can then replace or repair
hardware in the node you halted.
Figure 7-2 shows an HA pair where Controller A has failed and Controller B took over
services from the failing node.
Figure 7-2 Failover configuration

7.1.2 Characteristics of nodes in an HA pair

To configure and manage nodes in an HA pair, you need to know the characteristics that all
types of HA pairs have in common:
HA pairs are connected to each other. This connection cen be through an HA interconnect
that consists of adapters and cable, or, in systems with two controllers in the same
chassis, through an internal interconnect. The nodes use the interconnect to do the
following 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 following
conditions apply:
– Each node manages its own disks or array LUNs.
– Each node in takeover mode manages the disks or array LUNs of its partner. For
third-party storage, the partner node takes over read/write access to the array LUNs
owned by the failed node until the failed node becomes available again.
its
Chapter 7. Highly Available controller pairs
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