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Applies to SUSE Linux Enterprise High Availability Extension 11 SP4

Part III Storage and Data Replication

14 OCFS2

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 OpenAIS/Corosync and the Distributed Lock Manager (DLM).

15 DRBD

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 OpenAIS, DRBD supports distributed high-availability Linux clusters. This chapter shows you how to install and set up DRBD.

16 Cluster Logical Volume Manager (cLVM)

When managing shared storage on a cluster, every node must be informed about changes that are done to the storage subsystem. The Linux 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.

17 Storage Protection

The High Availability cluster stack's highest priority is protecting the integrity of data. This is achieved by preventing uncoordinated concurrent access to data storage: For example, Ext3 file systems are only mounted once in the cluster, OCFS2 volumes will not be mounted unless coordination with other cluster nodes is available. In a well-functioning cluster Pacemaker will detect if resources are active beyond their concurrency limits and initiate recovery. Furthermore, its policy engine will never exceed these limitations.

However, network partitioning or software malfunction could potentially cause scenarios where several coordinators are elected. If this so-called split brain scenarios were allowed to unfold, data corruption might occur. Hence, several layers of protection have been added to the cluster stack to mitigate this.

The primary component contributing to this goal is IO fencing/STONITH since it ensures that all other access prior to storage activation is terminated. Other mechanisms are cLVM2 exclusive activation or OCFS2 file locking support to protect your system against administrative or application faults. Combined appropriately for your setup, these can reliably prevent split brain scenarios from causing harm.

This chapter describes an IO fencing mechanism that leverages the storage itself, followed by the description of an additional layer of protection to ensure exclusive storage access. These two mechanisms can be combined for higher levels of protection.

18 Samba Clustering

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.

19 Disaster Recovery with Rear

Relax-and-Recover (formerly 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 just work out-of-the-box. Therefore it is essential to take preparations before any disaster happens.

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