Netezza appliance include necessary components to function seamlessly in the event of any hardware issue so that its availability is more that 99.99%. This is called Netezza high availability architecture that perform seamlessly in case of Netezza failover. There are two host in a cluster in all Netezza appliances so that if one fails other once can take over the task that is being carried out.
Netezza Failover – High Availability Architecture Overview
Netezza appliance uses the Linux-HA (high availability) and Distributed Replicated Block Device (DRBD) for the host cluster management and mirror the data between the hosts. High-Availability Linux (also called Linux-HA) provides the Netezza failover capabilities from a primary or active Netezza host to a secondary or standby Netezza host.
The main cluster management daemon in the Linux-HA solution is called Heartbeat. Heartbeat watches the hosts and manages the communication and status checks of services. Each service is a resource. Netezza groups the Netezza-specific services into the NPS resource group. When Heartbeat detects problems that imply a host failure condition or loss of service to the Netezza users, Heartbeat can initiate a failover to the standby host.
Distributed Replicated Block Device (DRBD)
Distributed Replicated Block Device (DRBD) is a block device driver that mirrors the content of block devices (hard disks, partitions, logical volumes, and other block devices) between the hosts.
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As par as the data storage is concerned, on third of every disk in the disk array stores the primary copy of user data, a third stores the mirror of primary copy of the data from another disk in the system, and another third is used as a temporary storage for any calculations.
In the event of the disk failure, the mirror copy will used and SPU will be updated with the data from the mirror copy. This is how the Netezza failover works in Netezza appliance.