Installing Oracle Linux - Expert Consolidation in Oracle Database 12c - page 174

The command creates a basic configuration file: /etc/multipath.conf and additionally loads the kernel
modules necessary for the correct operation of the package. Querying the mpathconf command you are shown the
successful execution:

# mpathconf
multipath is enabled
find_multipaths is disabled
user_friendly_names is enabled
dm_multipath module is loaded
multipathd is chkconfiged on

The next step is to review the newly created multipath.conf file, which is very similar to the format previously
used in Oracle Linux 5. The file still is subdivided into section, using the familiar curly braces. The most important
sections are these:

• Blacklist

• Defaults

• Devices

• Multipaths

The first section-blacklist {}-specifically excludes devices from being part of the multipathing configuration. This
is necessary for local devices that should not be part of the configuration. A new directive, find_multipaths provides
the administrator with some help in regards to blacklisted devices. Unlike the multipathing software in Oracle Linux 5,
which tried to create a new pseudo-device for every path it encountered, this behavior can be kept in check without
explicit blacklisting, using find_multipaths .
The next sections-defaults and device-are hugely vendor specific. Every storage vendor keeps information about
the multipath.conf file and their storage products in their support portals. It is strongly recommended to either
raise a call with your vendor or consult his documentation for the defaults and devices section. Interestingly the
defaults section does not need to be supplied at all; the package uses built-in variables for any value not specified
in the defaults-{} section. These defaults are documented in the /usr/share/doc/device-mapper-multipath- version /
multipath.conf file. On an example system, the following values were used:

defaults {
find_multipaths yes
user_friendly_names yes
}

All other values will be provided from the built-in defaults. This is not true for the devices-{} section, which
overrides the defaults for a specific array. For example, the below has been copied from the Oracle Linux 6.4
multipath.conf.defaults file, and can be used for an EMC-Clariion array:

devices {
device {
vendor "DGC"
product ".*"
product_blacklist "LUNZ"
path_grouping_policy group_by_prio
getuid_callout "/lib/udev/scsi_id --whitelisted --device=/dev/%n"
path_selector "round-robin 0"