Part III Storage and Data Replication #

The Distributed Lock Manager (DLM) in the kernel is the base component used by OCFS2, GFS2, Cluster MD, and cLVM to provide active-active storage at each respective layer.

Oracle Cluster File System 2 (OCFS2) is a general-purpose journaling file system that has been fully integrated since the Linux 2.6 Kernel. OCFS2 allows you to store application binary files, data files, and databases on devices on shared storage. All nodes in a cluster have concurrent read and write access to the file system. A user space control daemon, managed via a clone resource, provides the integration with the HA stack, in particular with Corosync and the Distributed Lock Manager (DLM).

Global File System 2 or GFS2 is a shared disk file system for Linux computer clusters. GFS2 allows all nodes to have direct concurrent access to the same shared block storage. GFS2 has no disconnected operating-mode, and no client or server roles. All nodes in a GFS2 cluster function as peers. GFS2 supports up to 32 cluster nodes. Using GFS2 in a cluster requires hardware to allow access to the shared storage, and a lock manager to control access to the storage.

SUSE recommends OCFS2 over GFS2 for your cluster environments if performance is one of your major requirements. Our tests have revealed that OCFS2 performs better as compared to GFS2 in such settings.

The distributed replicated block device (DRBD*) allows you to create a mirror of two block devices that are located at two different sites across an IP network. When used with Corosync, DRBD supports distributed high-availability Linux clusters. This chapter shows you how to install and set up DRBD.

When managing shared storage on a cluster, every node must be informed about changes that are done to the storage subsystem. The Logical Volume Manager 2 (LVM2), which is widely used to manage local storage, has been extended to support transparent management of volume groups across the whole cluster. Clustered volume groups can be managed using the same commands as local storage.

The cluster multi-device (Cluster MD) is a software based RAID storage solution for a cluster. Cluster MD provides the redundancy of RAID1 mirroring to the cluster. Currently, only RAID1 is supported now. This chapter shows you how to create and use Cluster MD.

A clustered Samba server provides a High Availability solution in your heterogeneous networks. This chapter explains some background information and how to set up a clustered Samba server.

Relax-and-Recover (“ReaR”, in this chapter abbreviated as Rear) is a disaster recovery framework for use by system administrators. It is a collection of Bash scripts that need to be adjusted to the specific production environment that is to be protected in case of disaster.

No disaster recovery solution will work out-of-the-box. Therefore it is essential to take preparations before any disaster happens.