IBM N Series, Hardware Manual

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Chapter 7. Highly Available controller pairs
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Figure 7-3 shows a standard HA pair with native disk shelves without Multipath Storage.
Figure 7-3 Standard HA pair with native disk shelves without Multipath Storage
In the example that is shown in Figure 7-3, cabling is configured without redundant paths to
disk shelves. If one controller loses access to disk shelves, the partner controller can take
over services. Takeover scenarios are described later in this chapter.
Setup requirements and restrictions for standard HA pairs
The following requirements and restrictions apply for standard HA pairs:
򐂰
Architecture compatibility: Both nodes must have the same system model and be running
the same firmware version. See the Data ONTAP Release Notes for the list of supported
systems, which is available at this website:
http://www.ibm.com/storage/support/nas
For systems with two controller modules in a single chassis, both nodes of the HA pair
configuration are in the same chassis and have internal cluster interconnect.
򐂰 Storage capacity: The number of disks must not exceed the maximum configuration
capacity. The total storage that is attached to each node also must not exceed the
capacity for a single node.
Clarification: After a failover, the takeover node temporarily serves data from all the
storage in the HA pair configuration. When the single-node capacity limit is less than
the total HA pair configuration capacity limit, the total disk space in a HA pair
configuration can be greater than the single-node capacity limit. The takeover node can
temporarily serve more than the single-node capacity would normally allow if it does not
own more than the single-node capacity.