Managing HP Serviceguard for Linux Ninth Edition, April 2009

before the package will be started. (In a cross-subnet configuration, all subnets
configured on that node, and identified as monitored subnets in the package
configuration file, must be available.)
The switching of relocatable IP addresses is shown in Figure 3-6 and Figure 3-7 .
Address Resolution Messages after Switching on the Same Subnet
When a relocatable IP address is moved to a new interface, either locally or remotely,
an ARP message is broadcast to indicate the new mapping between IP address and
link layer address. An ARP message is sent for each IP address that has been moved.
All systems receiving the broadcast should update the associated ARP cache entry to
reflect the change. Currently, the ARP messages are sent at the time the IP address is
added to the new system. An ARP message is sent in the form of an ARP request. The
sender and receiver protocol address fields of the ARP request message are both set to
the same relocatable IP address. This ensures that nodes receiving the message will
not send replies.
Unlike IPv4, IPv6 addresses use NDP messages to determine the link-layer addresses
of their neighbors.
Volume Managers for Data Storage
A volume manager lets you create units of disk storage that are more flexible than
individual disk partitions. These units can be used on single systems or in
high-availability clusters. HP Serviceguard for Linux uses the Linux Logical Volume
Manager (LVM) which creates redundant storage groups. This section provides an
overview of volume management with LVM. See “Creating the Logical Volume
Infrastructure ” (page 159) in Chapter 5 for information about configuring volume
groups, logical volumes, and file systems for use in Serviceguard packages.
In HP Serviceguard for Linux, the supported shared data storage type is disk arrays
which configure redundant storage in hardware.
In a disk array, the basic element of storage is a LUN, which already provides storage
redundancy via RAID1 or RAID5. Before you can use the LUNs, you must partition
them using fdisk.
In LVM, you manipulate storage in one or more volume groups. A volume group is
built by grouping individual physical volumes. Physical volumes can be disk partitions
or LUNs that have been marked as physical volumes as described below.
You use the pvcreate command to mark the LUN as physical volumes. Then you use
the vgcreate command to create volume groups out of one or more physical volumes.
Once configured, a volume group can be subdivided into logical volumes of different
sizes and types. File systems or databases used by the applications in the cluster are
mounted on these logical volumes. In Serviceguard clusters, volume groups are activated
by package control scripts when an application starts up, and they are deactivated by
package control scripts when the application halts.
Volume Managers for Data Storage 83