How HA pairs support nondisruptive operations and fault tolerance

HA pairs provide fault tolerance and let you perform nondisruptive upgrades and maintenance.

•	Fault tolerance

•	Nondisruptive software upgrades or hardware maintenance

The HA pair supplies nondisruptive operation and fault tolerance due to the following aspects of their configuration:

•	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.

•	Continually check whether the other node is functioning

•	Mirror log data for each other’s NVRAM or NVMEM

•	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 its partner's disks or array LUNs.

Note: Disk ownership is established by Data ONTAP or the administrator, rather than by which disk shelf the disk is attached to.

•	They own their spare disks, spare array LUNs, or both and do not share them with the other node.

•	They each have mailbox disks or array LUNs on the root volume that do the following tasks:

•	Maintain consistency between the pair

•	Continually check whether the other node is running or whether it has performed a takeover

•	Store configuration information that is not specific to any particular node