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:

  • Metadata redundancy. 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.

  • Data redundancy. Copies of each piece of data are stored across different storage nodes to ensure that the data is available even if some of the storage nodes are inaccessible.

    Note

    The redundancy is achieved by one of two methods: replication or erasure coding (for details, see Understanding Data Redundancy).

  • 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, you have not enabled HA for virtual machines and containers by means of the client server role during installation, and you want to enable it.

    In this case, continue reading this chapter.

  • You use Virtuozzo Storage with CLI management, you have enabled HA for virtual machines and containers by means of the client server role during installation, and you want to change the default resource relocation mode.

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

  • 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.