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HA Configuration : Understanding HA configuration : How the nodes in an HA pair provide redundancy
How the nodes in an HA pair provide redundancy
To configure and manage nodes in an HA pair, you should be familiar with how the nodes in the HA pair provide redundancy.
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The controllers in the HA pair are connected to each other either through an HA interconnect consisting 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:
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Continually check whether the other node is functioning
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Mirror log data for each other’s NVRAM or NVMEM
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Synchronize each other’s time
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They use two or more disk shelf loops, or third-party storage, in which the following conditions apply:
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Each node manages its own disks or array LUNs.
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Each node in takeover mode manages its partner's disks or array LUNs. 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.
Note: Disk ownership is established by Data ONTAP or the administrator, rather than by which disk shelf the disk is attached to.
For more information about disk ownership, see the Data ONTAP 7-ModeStorage Management Guide.
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They own their spare disks, spare array LUNs, or both and do not share them with the other node.
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They each have mailbox disks or array LUNs on the root volume that do the following tasks:
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Maintain consistency between the pair
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Continually check whether the other node is running or whether it has performed a takeover
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Store configuration information that is not specific to any particular node
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They can reside on the same Windows domain or on different domains.

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