HP XC System Software Administration Guide Version 3.2

19 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 227)
• “Installing Software RAID on the Head Node” (page 227)
• “Installing Software RAID on Client Nodes” (page 227)
• “Examining a Software RAID Array” (page 228)
• “Error Reporting” (page 229)
• “Removing Software RAID from Client Nodes” (page 229)
19.1 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.
19.1.1 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.
19.1.2 Software RAID-1
Software RAID-1 is also known as mirroring. Data is written to two disks, one a mirror of the
other.
19.2 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.
19.3 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.
19.1 Overview of Software RAID 227