HSNs are instances you can deploy along with your TPA nodes to join your TPA configuration in case of node failure. This helps to avoid situations when NFR is unable to provision a replacement node, such as when there are insufficient resources available in a placement group. The use of HSNs improves availability and allows the system to recover easier from node failures.
Teradata recommends provisioning HSNs when deploying a Teradata ecosystem or deploying Vantage separately. You can also provision HSNs that to join the already deployed instances. There is a higher risk of failure with this method.
If a node failure occurs, Fallback is initiated only when NFR fails to replace a failed node. This happens regardless if HSNs are provisioned. Fallback is enabled by default when you deploy a Vantage instance in the public cloud. The NFR process automatically detaches the storage from the failed node and attaches the storage to the replacement instance. While the AMPs migrate to the HSNs, Vantage is not operational as TPA resets are occurring.
Guidelines and Limitations
- HSNs can be provisioned for all license tiers, including Developer.
- The total number of TPA nodes and HSNs cannot exceed the instance limit of the Vantage license tier you are using.
- When determining the number of HSNs to provision, do not exceed the number of deployed database nodes. For example, a four node system cannot have more than four HSNs.
- You can decide the number of HSNs required based on your requirements. Teradata recommends at least one HSN for every 16 Nodes of a System and a minimum of two HSN nodes for a 32 node system.
Having at least two HSN nodes for a system will take advantage by quickly replacing two new nodes when two nodes had issues and lost contact with the system at the same time.
Hot Standby Nodes Provisioning
If you provision HSNs when deploying a Vantage instance for a Base, Advanced, or Enterprise license tier, you pay extra hardware and software fees for HSNs, whether the database is running or not.
To provision HSNs, follow these instructions:
| Action | Instructions |
|---|---|
| Provision an HSN at deployment |
If you do not want to provision any HSNs, set the Number of Hot Standby Nodes parameter to 0 at deployment. |
| Provision an HSN after deployment | Provisioning Hot Standby Nodes after Deployment |