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Configuring your Environment for Software RAID
Configuring the Environment
Chapter 366
Configuring the Environment
After setting up the hardware as described in the Extended Distance
Cluster Architecture section and installing the Extended Distance
Cluster software, complete the following steps to enable Software RAID
for each package. Subsequent sections describe each of these processes in
detail.
1. Configure multipath for storage
In the Extended Distance Cluster setup described in figures 1 and 2,
a node has multiple paths to storage. With this setup each LUN
exposed from a storage array shows up as two devices on every node.
There are two device entries in the /dev directory for the same LUN
where each device entry will pertain to a single path to that LUN.
When a QLogic driver is installed and configured for multipath, all
device names leading to the same physical device will be merged and
only one device entry will appear in their place. This happens for
devices from both the storage systems. Creating these multiple links
to the storage device ensures that each node is not dependent only on
one link to write data to that storage device. For more information on
configuring multipath, see “Configuring Multiple Paths to Storage”
on page 69.
2. Configure persistent device names for storage devices
Once the multipath has been configured, you need to create
persistent device names using udev. In cases of disk or link failure
and subsequent reboot, it is possible that device names are renamed
or reoriented. Since the MD mirror device starts with the names of
the component devices, a change in the device name prevents the MD
mirror from starting. To avoid this problem, HP requires that you
make the device names persistent. For more information on
configuring persistent device names, see “Using Persistent Device
Names” on page 71.
3. Create the MD mirror device
To enable Software RAID in your environment, you need to first
create the mirror setup. This implies that you specify two disks to
create a Multiple Device (MD). When configuring disks in RAID 1
level, use a disk or LUN from each datacenter as one mirror half. Be
sure to create disk sets of the same size as they need to store data