Clustered-File-System service considerations

The Clustered-File-System service gives storage space to other services in an HCI system.

Multiple service instance types

Each instance of the Clustered-File-System service can be one of these types:

• Data Node: Stores data
• Name Node: Tracks the data stored in Data Nodes
• Journal Node: Tracks changes made by the Name Nodes

You can run multiple different Clustered-File-System service instance types on an HCI instance. For example, a single HCI instance can run both a Journal Node and a Data Node instances of the Clustered-File-System service.

You cannot run multiple Clustered-File-System service instances of the same type on an HCI instance. For example, a single HCI instance cannot run two Data Node instances.

Deployment modes

The Clustered-File-System service can be deployed in either of these modes:

• High Availability (HA) Mode: In HA mode, the Clustered-File-System service can retain its stored data in the event that a Name Node instance fails or becomes corrupt.
• Non-HA Mode: In Non-HA mode, the Clustered-File-System service has a single Name Node instance. If this instance fails or becomes corrupt, all data stored by the Clustered-File-System service is lost.

The service's deployment mode is determined based on the number of service type instances you have when you initially deploy the service. After the deployment mode is set, you cannot change it without losing all data stored by the Clustered-File-System service.

Initial deployment requirements: HA mode

To deploy the Clustered-File-System service in HA mode, you need at least three HCI instances.

Upon initial deployment of the service, you need to configure the service to run:

• Exactly two Name Node instances
• Exactly three Journal Node instances

You can run any number of Data Node instances. You need at least one to be able to store data. For HA mode, the recommended minimum is three.

Initial deployment requirements: Non-HA mode

To deploy the Clustered-File-System service in Non-HA mode, you need only one HCI instance.

Upon initial deployment of the service, you need to configure the service to run:

• Exactly one Name Node instance
• Zero Journal Node instances

You can run any number of Data Node instances. You need at least one to be able to store data.

Scaling and moving the service

When scaling or moving Name Node or Journal Node service instances, you need to perform only one operation at time.

For example, to move a Name Node from one HCI instance to another, you need to:

1. Run a service operation to remove an instance of the Name Node service type.
2. Wait for the operation to finish.
3. Run a service operation to start a new instance of the Name Node service type.
4. Wait for the operation to finish.

When running the Clustered-File-System service in HA mode, you need at least two Journal Node instances running. Scaling the service such that you have zero or one Journal Node instances causes the service to become unresponsive.

You can scale or move as many Data Node instances as necessary.

Changing deployment modes

When you initially deploy the Clustered-File-System service, it is deployed in either HA or Non-HA mode, depending on the number of service instances types you initially configure the service to run.

You can change the Clustered-File-System deployment mode after the service is initially deployed, however this needs a complete redeployment of the service.

To switch from one deployment mode to another:

1. Scale Clustered-File-System to run on zero instances in the system.
2. Configure and run a service scale task to scale Clustered-File-System to the applicable number of service type instances.
   Important: Name Node and Journal Node types must be scaled together in a single operation.