HP Serviceguard Extended Distance Cluster for Linux A.11.20.20 Deployment Guide, August 2013

in a mirror being created of a size equal to the smaller of the two disks. Be sure to create the mirror
using the persistent device names of the component devices.
As mentioned earlier, the first step for enabling Software RAID in your environment is to create the
Multiple Disk (MD) device using two underlying component disks. This MD device is a virtual device
which ensures that any data written to it is written to both component disks. As a result, the data
is identical on both disks that make up the MD device.
This section describes how to create an MD device. This is the only step that you must complete
before you enable Software RAID for a package. The other RAID operations are needed only
during maintenance or during recovery process after a failure has occurred.
NOTE: For all the steps in the subsequent sections, all the persistent device names, and not the
actual device names, must be used for the two component disks of the MD mirror.
Do not create partitions on MD devices. Use of partitioned MD device is not supported.
3.3.3.1 Creating and Assembling an MD Device
This example shows how to create the MD device /dev/md0, you must create it from a LUN of
storage device 1 (/dev/hpdev/sde ) and another LUN from storage 2 (/dev/hpdev/sdf ) .
To create an MD device:
1. Run the following command:
# mdadm --create --verbose /dev/md0 --name=0 --level=1
--raid-devices=2 /dev/hpdev/sde /dev/hpdev/sdf
2. To have the name of MD device consistent across the nodes, copy the output of # mdadm
–Db /dev/md0 command to /etc/mdadm.conf file:
mdadm –Db /dev/md0
The output will be as follows:
ARRAY /dev/md0 metadata=1.2 name=node1.ind.hp.com:0
UUID=354b6919:e7db657c:1864a2c0:481b5f36
NOTE: Ensure that you copy the output to /etc/mdadm.conf file for each node.
Once the new RAID device, /dev/md0, is created on one of the cluster nodes, you must assemble
it on the nodes where the package must run.
To enable write intent internal bitmap on MD device, see “Enabling and Disabling Write Intent
Internal Bitmap” (page 50).
NOTE: Use of write intent internal bitmap is supported on the following patches and later:
• SGLX_00455 on Red Hat Enterprise Linux 5
• SGLX_00456 on Red Hat Enterprise Linux 6
• SGLX_00457 on SUSE Linux Enterprise Server 11
You create an MD device only once and you can manage other functions using the serviceguard-xdc
scripts.
To assemble the MD device, complete the following procedure:
1. Stop the MD device on the node where you created it, by running the following command:
# mdadm -S /dev/md0
2. On the other nodes, do the following:
3.3 Configuring the Storage Environment 25