AN!Wiki :: RHCS 2 Overview

Note: This is a dumping ground for me to use while reading more into detail on RHCS v2 clustering.

Overview

These notes came from this Red Hat PDF (single, multiple HTML pages).

Types

Four major types of clusters:

Storage (GFS/GFS2)
High availability (aka "Failover Cluster", High Availability Systems Management)
Load balancing (Linux Virtual Server)
High performance (aka "Computational Cluster" or "Grid Computing")

Implemented clusters can combine the above types.

Cluster infrastructure - Provides fundamental functions for nodes to work together as a cluster: configuration-file management, membership management, lock management, and fencing.
High-availability Service Management - Provides failover of services from one cluster node to another in case a node becomes inoperative.
Cluster administration tools - Configuration and management tools for setting up, configuring, and managing a Red Hat cluster. The tools are for use with the Cluster Infrastructure components, the High-availability and Service Management components, and storage.
Linux Virtual Server (LVS) - Routing software that provides IP-Load-balancing. LVS runs in a pair of redundant servers that distributes client requests evenly to real servers that are behind the LVS servers.

Optional components that are outside the scope of RHCS are:

GFS2 - Global File System v2 provides a cluster file system for use with Red Hat Cluster Suite. GFS/GFS2 allows multiple nodes to share storage at a block level as if the storage were connected locally to each cluster node.
Cluster Logical Volume Manager (CLVM) - Provides volume management of cluster storage.
Global Network Block Device (GNBD) - An ancillary component of GFS/GFS2 that exports block-level storage to Ethernet. This is an economical way to make block-level storage available to GFS2.

A cluster service can run on only one cluster node at a time to maintain data integrity.
Failover domains are not required for operation. A failover domain is a subset of cluster nodes that are eligible to run a particular cluster service.
GFS/GFS2 supports up to 16 nodes. It works, but is not supported on a single node (not counting failed nodes leaving just one node alive). Partitions can be, in theory, up to 8 EB in size, but are only supported up to 25 TB. GFS partitions must be created on a CLVM-backed linear or mirrored logical volume.
Change needs to be made to /etc/lvm/lvm.conf. Specifically, locking_type must be set to 3. This can be done by calling lvmconf --enable-cluster.
GNDB is designed to be an GFS-specific implementation of NDB. It's useful when more robust storage, like fibre-channel, is not needed of not affordable.

ccs_tool: Cluster Configuration System Tool
- a program for making online updates to the cluster configuration file. It provides the capability to create and modify cluster infrastructure components (for example, creating a cluster, adding and removing a node). For more information about this tool, refer to the ccs_tool(8) man page.
cman_tool: Cluster Management Tool
- a program that manages the CMAN cluster manager. It provides the capability to join a cluster, leave a cluster, kill a node, or change the expected quorum votes of a node in a cluster. For more information about this tool, refer to the cman_tool(8) man page.
fence_tool: a program used to join or leave the default fence domain. Specifically, it starts the fence daemon (fenced) to join the domain and kills fenced to leave the domain. For more information about this tool, refer to the fence_tool(8) man page.
clustat: Cluster Status Utility
- The clustat command displays the status of the cluster. It shows membership information, quorum view, and the state of all configured user services. For more information about this tool, refer to the clustat(8) man page.
clusvcadm: Cluster User Service Administration Utility
- The clusvcadm command allows you to enable, disable, relocate, and restart high-availability services in a cluster. For more information about this tool, refer to the clusvcadm(8) man page.

These notes came from this Red Hat PDF (single, multiple HTML pages

Any questions, feedback, advice, complaints or meanderings are welcome.
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