HSNs are instances you can optionally deploy along with your TPA nodes to join your TPA configuration in case of node failure. This avoids 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 more easily recover from node failures.
Teradata recommends deploying HSNs when deploying a Teradata ecosystem or deploying Teradata Database separately. You can also provision HSNs that will join the already deployed instances, although 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 Teradata Database 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, Teradata Database 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 Teradata Database 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 4 node system cannot have more than 4 HSNs.
- Teradata recommends provisioning 1 HSN for up to 32 nodes and 2 HSNs for 33 to 64 nodes.
Information about Provisioning Hot Standby Nodes
If you provision HSNs when deploying a Teradata Software for AWS instance for Base, Advanced or Enterprise license tier, you pay extra hardware and software costs for HSNs, whether the database is running or not. If you provision HSNs when deploying an instance using the BYOL listing in the AWS Marketplace, you pay only for the extra hardware cost for the HSNs, whether the database is running or not.
| 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 |