Single point of failure analysis for HA pairs

Different individual hardware components and cables in the storage system are single points of failure, but an HA configuration can eliminate these points to improve data availability.

Hardware components Single point of failure How storage failover eliminates single point of failure
Stand-alone HA pair
Controller Yes No If a controller fails, the node automatically fails over to its partner node. The partner (takeover) node serves data for both of the nodes.
NVRAM Yes No If an NVRAM adapter fails, the node automatically fails over to its partner node. The partner (takeover) node serves data for both of the nodes.
CPU fan Yes No If the CPU fan fails, the node automatically fails over to its partner node. The partner (takeover) node serves data for both of the nodes.
Multiple NICs with interface groups (virtual interfaces) Maybe, if all NICs fail No If one of the networking links within an interface group fails, the networking traffic is automatically sent over the remaining networking links on the same node. No failover is needed in this situation.

If all the NICs in an interface group fail, the node automatically fails over to its partner node if failover is enabled for the interface group.

Single NIC Yes No If a NIC fails, the node automatically fails over to its partner node if failover is enabled for the NIC.
FC-AL adapter or SAS HBA Yes No If an FC-AL adapter for the primary loop fails for a configuration without multipath HA, the partner node attempts a takeover at the time of failure. With multipath HA, no takeover is required.

If the FC-AL adapter for the secondary loop fails for a configuration without multipath HA, the failover capability is disabled, but both nodes continue to serve data to their respective applications and users, with no impact or delay. With multipath HA, failover capability is not affected.

FC-AL or SAS cable (controller-to-shelf, shelf-to-shelf ) No, if dual-path cabling is used No If an FC-AL loop or SAS stack breaks in a configuration that does not have multipath HA, the break could lead to a failover, depending on the shelf type. The partnered nodes invoke the negotiated failover feature to determine which node is best for serving data, based on the disk shelf count. When multipath HA is used, no failover is required.
Disk shelf module No, if dual-path cabling is used No If a disk shelf module fails in a configuration that does not have multipath HA, the failure could lead to a failover. The partnered nodes invoke the negotiated failover feature to determine which node is best for serving data, based on the disk shelf count. When multipath HA is used, there is no impact.
Disk drive No No If a disk fails, the node can reconstruct data from the RAID4 parity disk. No failover is needed in this situation.
Power supply Maybe, if both power supplies fail No Both the controller and disk shelf have dual power supplies. If one power supply fails, the second power supply automatically kicks in. No failover is needed in this situation. If both power supplies fail, the node automatically fails over to its partner node, which serves data for both nodes.
Fan (controller or disk shelf) Maybe, if both fans fail No Both the controller and disk shelf have multiple fans. If one fan fails, the second fan automatically provides cooling. No failover is needed in this situation. If both fans fail, the node automatically fails over to its partner node, which serves data for both nodes.
HA interconnect adapter Not applicable No If an HA interconnect adapter fails, the failover capability is disabled but both nodes continue to serve data to their respective applications and users.
HA interconnect cable Not applicable No The HA interconnect adapter supports dual HA interconnect cables. If one cable fails, the heartbeat and NVRAM data are automatically sent over the second cable with no delay or interruption.

If both cables fail, the failover capability is disabled but both nodes continue to serve data to their respective applications and users.