Changing the size of a IBM Spectrum Scale cluster

After you deploy a IBM® Spectrum Scale cluster, you can increase or decrease the size of the IBM Spectrum Scale quorum nodes or IBM Spectrum Scale NSD nodes.

Before you begin

If you are increasing the IBM Spectrum Scale cluster size, the type of node that the system adds depends on how many quorum nodes currently exist in the IBM Spectrum Scale cluster:

If the number of quorum nodes is less than the number originally requested, the template adds quorum nodes to the IBM Spectrum Scale cluster, up to the number requested.
If the number of quorum nodes is equal to the number originally requested, the template adds NSD nodes to the IBM Spectrum Scale cluster.

If you are decreasing the IBM Spectrum Scale cluster size, you can remove either quorum nodes or NSD nodes. To avoid making the IBM Spectrum Scale cluster or file system unavailable, when you are removing nodes, you must ensure that both of these rules are satisfied:

If you are removing a quorum node, you must ensure that the GPFS cluster does not lose quorum after the node is removed. A IBM Spectrum Scale cluster achieves quorum if most of quorum nodes are up. If the IBM Spectrum Scale cluster loses quorum, the entire cluster becomes unavailable. For example, if the IBM Spectrum Scale cluster has three quorum nodes, quorum is achieved when 2 are more quorum nodes are up. If you remove one node, quorum is maintained. If you remove two nodes, then quorum is lost.
If you are removing a quorum or NSD node, the maximum number of nodes you can remove depends on the replication factor of the IBM Spectrum Scale file system. The number of nodes you remove must be less than the replication factor. If you remove more than the replication factor, the entire IBM Spectrum Scale file system becomes unavailable. For example, if the replication factor is 2, you can remove a maximum of 1 node from the cluster.

In both cases, whether increasing or decreasing the cluster size, the following requirements must be met before you change the cluster size:

The IBM Spectrum Scale cluster is in Active state.
All of the IBM Spectrum Scale nodes are in active state.

Procedure

To increase the size of the cluster:
1. Log in to IBM Spectrum Cluster Foundation Community Edition management node as a root user.
2. From the Clusters tab, select Clusters from the menu.
3. Select the IBM Spectrum Scale cluster that you want to change and click Modify Cluster Size.
4. Select the GPFSServer tier and increase or decrease the number of servers that you want in the cluster.
5. Click Apply to apply your changes to the cluster.
To decrease the size of the cluster:
1. Log in to IBM Spectrum Cluster Foundation Community Edition management node as a root user.
2. From the Clusters tab, select Clusters from the menu.
3. Select the IBM Spectrum Scale cluster that you want to change and click the Servers tab in the bottom pane.
4. Select the nodes to remove, and click the Remove from Cluster button.
5. Input the reason for removing the nodes and select Yes.

Results

If the number of servers was increased, then the new servers are added as either quorum or NSD nodes, and their disks are added to IBM Spectrum Scale file system.

If the number of servers was decreased, then the selected nodes are removed from the GPFS cluster, and their disks are removed from the IBM Spectrum Scale file system.

What to do next

Verify that the IBM Spectrum Scale cluster is running correctly and that the IBM Spectrum Scale nodes are working correctly. To verify that the nodes are working correctly, log in to the first IBM Spectrum Scale quorum node using ssh. The first IBM Spectrum Scale quorum node is defined by the GPFS_Primary_Quorum_Node variable. Then, complete the following verification tasks:

To verify that the total number of quorum nodes reflects the increased or decreased number of servers, run the following command:
```
# mmgetstate -s
```
To verify that all servers are in active state, run the following command:
```
# mmgetstate -a -L
```
Verify that the correct number of servers are added to the gpfsmntdata file system, by ensuring that each disk comes from each IBM Spectrum Scale node. Run the following command:
```
# mmlsfs gpfsmntdata -d
```
To verify that all nodes mount the IBM Spectrum Scale file system, run the following command:
```
# mmlsmount gpfsmntdata -L
```