HP XC System Software Administration Guide Version 3.1

18 Managing Software RAID Arrays
The HP XC system can mirror data on a RAID array. This chapter addresses the following topics:
• “Overview of Software RAID” (page 211)
• “Installing Software RAID on the Head Node” (page 211)
• “Installing Software RAID on Client Nodes” (page 211)
• “Examining a Software RAID Array” (page 212)
• “Error Reporting” (page 213)
• “Removing Software RAID from Client Nodes” (page 213)
18.1 Overview of Software RAID
A Redundant Array of Independent Disks (RAID) is a method for distributing data across multiple disk
partitions. There are several types of RAID configurations. The HP XC System Software enables you to
use Software RAID-0 or Software RAID-1 on two or more disk partitions.
The HP XC system implements RAID through software, not hardware. The operating system on the node
handles the software RAID operations.
Logical devices, designated as /dev/mdn, are created from two or more partitions. These logical devices
are the array.
Partitions in an array must be the same size.
The requirements for implementing software RAID-1 on an HP XC system depend on the node:
Head node Software RAID-1 requires a minimum of two disks on the head node. You can add
additional disks after the initial installation.
Client node A client node is any node that is not the head node. Software RAID requires a minimum
of two same-sized disks. You can configure additional disks after the initial installation.
18.1.1 Software RAID-0
Software RAID-0 is also known as striping. A stripe is a contiguous sequence of disk blocks. The partitions
on the disks are organized into stripes and interleaved.
18.1.2 Software RAID-1
Software RAID-1 is also known as mirroring. Data is written to two disks, one a mirror of the other.
18.2 Installing Software RAID on the Head Node
You can install software RAID during the kickstart process of the installation of the HP XC System
Software. If two or more disks are present on the head node, the kickstart process automatically asks
if you want to install the HP XC System Software with Software RAID-1. For more information about the
kickstart process, see the HP XC System Software Installation Guide.
NOTE: The kickstart process does not allow the /boot partition on a CP6000 system's head node to
be installed as a software RAID array.
18.3 Installing Software RAID on Client Nodes
The use of software RAID is not automatic or required; you must enable it for each node. Installing HP
XC System Software using software RAID requires you to edit a configuration file and run the
cluster_config utility to update the system configuration database with node role assignments, start
all services on the head node, and re-create or update the golden system image.
Use the following procedure to install software RAID on client nodes:
1. Log in as superuser (root) on the head node.
2. Generate a list of nodes on whose disks you will install the HP XC System Software with software
RAID.
18.1 Overview of Software RAID 211