IBM N Series, Hardware Manual

Page: 103 / 368

Chapter 7. Highly Available controller pairs
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7.3.1 Configuration variations for standard HA pair configurations
The following configuration variations are supported for standard HA pair configurations:
򐂰 Asymmetrical configurations: In an asymmetrical standard HA pair configuration, one
node has more storage than the other. This configuration is supported if neither node
exceeds the maximum capacity limit for the node.
򐂰
Active/passive configurations: In this configuration, the passive node has only a root
volume. The active node has all the remaining storage and services all data requests
during normal operation. The passive node responds to data requests only if it takes over
for the active node.
򐂰 Shared loops or stacks: If your standard HA pair configuration is using software-based
disk ownership, you can share a loop or stack between the two nodes. This is useful for
active/passive configurations.
򐂰 Multipath storage: Multipath storage for HA pair configurations provides a redundant
connection from each node to every disk. It can prevent some types of failovers.
7.3.2 Preferred practices for HA pair configurations
Adhere to the following preferred practices to ensure that HA pair storage systems achieve
maximum uptime:
򐂰 Make sure that the HA pair storage systems and shelves are on separate power supplies
or grids. This configuration prevents a single power outage from affecting both controller
units and shelves.
򐂰 Use VIFs to provide redundancy and improve the availability of network communication.
The virtual interfaces are set up during initial installation or the subsequent initiation of
setup.
򐂰 Maintain a consistent configuration between HA pair nodes, such as Data ONTAP
versions. An inconsistent HA pair storage system configuration is often related to failover
problems.
򐂰 Test the failover capability periodically (for example, during planned maintenance) to
ensure an effective HA pair storage system configuration.
򐂰 Follow the documented procedures in the upgrade guide when you are upgrading HA pair
storage systems.
򐂰
Make sure that HA pair nodes have sufficient resources to adequately support workload
during takeover mode.
򐂰 Periodically use the HA pair configurations checker to help ensure that failovers are
successful.
򐂰
Make sure that the
/etc/rc
file is correctly configured, as shown in Example 7-1 on
page 84.
Attention: Use VIFs with HA pairs to reduce single points of failure (SPOFs). If you do not
want to configure your network for use in an HA pair when you run the
setup command for
the first time, you can configure it later. You can do so by running the setup command
again, or by using the ifconfig command and editing the /etc/rc file manually. However,
you must provide at least one local IP address to exit setup.