HP Serviceguard Extended Distance Cluster for Linux A.12.00.00 Deployment Guide, March 2014

3 Configuring your Environment for Software RAID
The previous chapters discussed conceptual information on disaster recovery architectures and
procedural information on creating an extended distance cluster. This chapter discusses the
procedures you need to follow to configure Software RAID in your extended distance cluster.
3.1 Understanding Software RAID
Redundant Array of Independent Disks (RAID) is a mechanism that provides storage fault tolerance
and, occasionally, better performance. Software RAID is designed on the concept of RAID 1. RAID
1 uses mirroring where data is written to two disks at the same time.
The serviceguard-xdc product uses the following:
• Multiple Device (MD) driver and its associated tool mdadm to implement Software RAID. For
more information on Linux Software RAID, see The Software-RAID HOWTO available at http://
www.tldp.org/HOWTO/Software-RAID-HOWTO.html.
Or
• VxVM mirroring. For more information about VxVM mirroring, see Veritas Storage Foundation
Administrator's Guide available at https://sort.symantec.com/documents/doc_details/sfha/
6.0.1/Linux/ProductGuides.
With Software RAID, two disks (or disk sets) are configured so that the same data is written on
both disks as one "write transaction". So if data from one disk set is lost, or if one disk set is
rendered unavailable, the data is always available from the second disk set. As a result, high
availability of data is guaranteed. In an extended distance cluster, the two disk sets are in two
physically separated locations, so if one location becomes unavailable, the other location still has
the data.
To enable Software RAID in your extended distance cluster, you need to complete the following:
1. Install the extended distance cluster software.
2. Configure packages that will use Software RAID.
3.2 Prerequisites
Following are the prerequisites for installing serviceguard-xdc version A.12.00.00:
• HP Serviceguard for Linux A.12.00.00
• Ensure that mdadm and udev rpms are installed on your system.
1
• Network Time Protocol (NTP) — All nodes in the cluster should point to the same NTP server.
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3.3 Configuring the Storage Environment
After setting up the hardware as described in the Extended Distance Cluster Architecture section
and installing the Extended Distance Cluster software, see the following sections that describe each
of these processes in detail.
3.3.1 Configuring the Storage
This section describes the configuration changes recommended for both single path and multiple
paths to storage as described in Figure 3.
1. In serviceguard-xdc environment, if you have configured with VxVM disk group mirrored this is not required.
3.1 Understanding Software RAID 21