8. Managing High Availability Clusters¶

This chapter explains managing high availability (HA) for servers that participate in Virtuozzo Storage clusters.

High availability keeps virtual machines, containers, and iSCSI targets operational even if the node they are located on fails. In such cases, the affected virtual environments continue working on other, healthy nodes in the cluster. High availability is ensured by:

• Replication of metadata servers. For a Virtuozzo Storage cluster to function, not all but just the majority of MDS servers must be up. By setting up multiple MDS servers in the cluster you will make sure that if an MDS server fails, other MDS servers will continue controlling the cluster.
• Replication of data. All data chunks are replicated and the replicas are kept on different chunk servers. If a chunk server fails, other chunk servers will continue providing the data chunks that were stored on the failed server.
• Monitoring of node health.

You may need to follow different instructions in this chapter based on your scenario which can be one of these:

• You use Virtuozzo Storage with CLI management and you need to configure HA.

  In this case, continue reading this chapter.

• You use Virtuozzo Storage with GUI management, you have not assigned iSCSI network roles or created S3 clusters yet in the Virtuozzo Storage management panel, and you want to configure HA manually (e.g., to manually choose a resource relocation mode).

  In this case, continue reading this chapter.

• You use Virtuozzo Storage with GUI management, you have assigned the network role “ISCSI” to a node’s network interface or joined a node to an S3 cluster in the Virtuozzo Storage management panel, and you want to change the default resource relocation mode.

  In this case, HA in the round-robin mode is automatically enabled for virtual machines and containers on the node. To change the resource relocation mode, e.g., to DRS, follow the instructions in Configuring Resource Relocation Modes on Nodes Participating in S3 or iSCSI Export.