Table of Contents
This chapter describes using DRBD as replicated storage for Red Hat Cluster high availability clusters.
![]() | Note |
---|---|
This guide uses the unofficial term Red Hat Cluster to refer to a product that has had multiple official product names over its history, including Red Hat Cluster Suite and Red Hat Enterprise Linux High Availability Add-On. |
Red Hat Cluster, originally designed primarily for shared
storage clusters, relies on node fencing to prevent concurrent,
uncoordinated access to shared resources. The Red Hat Cluster
fencing infrastructure relies on the fencing daemon fenced
, and
fencing agents implemented as shell scripts.
Even though DRBD-based clusters utilize no shared storage resources and thus fencing is not strictly required from DRBD’s standpoint, Red Hat Cluster Suite still requires fencing even in DRBD-based configurations.
The resource group manager ( rgmanager
, alternatively clurgmgr
) is
akin to Pacemaker. It serves as the cluster management suite’s primary
interface with the applications it is configured to manage.
A single highly available application, filesystem, IP address and the like is referred to as a resource in Red Hat Cluster terminology.
Where resources depend on each other — such as, for example, an NFS export depending on a filesystem being mounted — they form a resource tree, a form of nesting resources inside another. Resources in inner levels of nesting may inherit parameters from resources in outer nesting levels. The concept of resource trees is absent in Pacemaker.
Where resources form a co-dependent collection, that collection is called a service. This is different from Pacemaker, where such a collection is referred to as a resource group.
The resource agents invoked by rgmanager
are similar to those used by
Pacemaker, in the sense that they utilize the same shell-based
API as defined in the Open Cluster Framework (OCF), although Pacemaker
utilizes some extensions not defined in the framework. Thus in theory,
the resource agents are largely interchangeable between Red Hat
Cluster Suite and Pacemaker — in practice however, the two cluster
management suites use different resource agents even for similar or
identical tasks.
Red Hat Cluster resource agents install into the /usr/share/cluster
directory. Unlike Pacemaker OCF resource agents which are by
convention self-contained, some Red Hat Cluster resource agents are
split into a .sh
file containing the actual shell code, and a
.metadata
file containing XML resource agent metadata.
DRBD includes a Red Hat Cluster resource agent. It installs into the
customary directory as drbd.sh
and drbd.metadata
.