Multipath.confis the configuration file for the multipath daemon, multipathd.
This file overrides the built-in configuration table for multipathd. Any line in the file that begins with the first non-white-space character # is a comment line. Empty lines should be ignored.
By default, DMMP is supported on certain machine-type models of the IBM DS3000/DS5000 subsystems. However, IBM recommends overriding the default settings using the multipath.conf file to ensure that the DMMP settings are as under:
To set up the multipath.conf file, complete the following steps:
1. Copy the sample multipath.conf from the appropriate directory, depending on whether the Linux operating system is Redhat RHEL or Novell SLES, to the /etcdirectory.
v For SLES, the file is named multipath.conf.synthetic and is stored in this directory: /usr/share/doc/packages/multipath-tools/.
v For RHEL, the file is called multipath.conf.defaults and is stored in this directory: /usr/share/doc/device-mapper-multipath-0.4.9/.
2. Rename the file multipath.conf.
3. Make the configuration changes described in this section to the new
/etc/multipath.conffile. The content of the sample multipath.conf file varies, depending on whether it is from SLES or RHEL kernels.
Note: All entries for multipath devices are commented out initially. To uncomment, remove the first character (#) from that section. You must uncomment the three sections - default, blacklist, and devices.
The configuration file is divided into five sections:
defaults
Specifies all of the default values.
blacklist
Blacklists new installations. The default blacklist is listed in the commented-out section of the/etc/multipath.conf file. Blacklist the device mapper multipath by WWID if you do not want to use this functionality.
blacklist_exceptions
Specifies any exceptions to the items in the blacklist section.
devices
Lists all of the multipath devices with their matching vendor and product values.
multipaths
Lists all of the multipath devices with their matching WWID values.
To determine the attributes of a multipath device, check the multipaths section of the /etc/ multipath.conf file; then the devices section; and then the defaults section. Depending on the version of the Linux kernel, the devices section of the sample multipath.conf file might already have settings defined for your storage subsystem model product ID. All you need to do is verify that the settings match the recommended settings listed below. Otherwise, you have to manually enter the devices settings for your subsystem model product ID. If you have multiple
storage subsystems with different product IDs connected to the Linux host, add the device settings for each storage subsystem product ID in the devices section of the
/etc/ multipath.conf file. Sample settings for DS3500 (product ID 1746) and DS5100/DS5300 (product ID 1818) in the devices section of the multipath.conf file in SLES operating systems are shown below:
Note: If the Product ID exceeds four characters, use only the first four characters.
In the following example, although the Product ID is '1746 FAStT', the product is specified as '1746'. Similarly, '1818 FAStT' is specified as '1818'.
Devices { device {
vendor "IBM"
product "1746"
path_grouping_policy group_by_prio
getuid_callout "/lib/udev/scsi_id -g -u -d /dev/%n"
path_selector "round-robin 0"
getuid_callout "/lib/udev/scsi_id -g -u -d /dev/%n"
path_selector "round-robin 0"
Sample settings for DS3500 (product ID 1746) and DS5100/DS5300 (product ID 1818) in the devices section of the multipath.conf file in RHEL operating systems are shown below:
device {
If you have Access LUN (sometimes referred to as UTM LUN) mapped to the host partitions, include an entry in the blacklist section of the/etc/multipath.conf file, so that the file is not managed by the DMMP. The Storage manager host software uses the Access LUN for in-band management of the storage subsystem. The entries should follow the pattern of the following example:
blacklist { device { vendor "*"
product "Universal Xport"
}
The following table describes the attributes and values in the devices section of the /etc/multipath.conf file.
Table 27. Attributes and parameter values in the multipath.conf file
Attribute Parameter value Description
path_grouping_policy group_by_prio This attribute determines the path grouping policy to be applied to this specific vendor and product storage.
prio rdac This attribute sets the
program and arguments to determine the path priority routine. The specified routine should return a numeric value specifying the relative priority of this path. Higher numbers have a higher call out and obtain a unique path identifier.
polling_interval 5 This attribute determines the
interval between two path checks, in seconds.
path_checker rdac This attribute establishes the
method used to determine the state of the path.
Table 27. Attributes and parameter values in the multipath.conf file (continued)
Attribute Parameter value Description
path_selector "round-robin 0" This attribute determines the path selector algorithm to use when there is more than one path in a path group.
hardware_handler "1 rdac" This attribute determines the hardware handler to use for handling device-specific knowledge.
failback immediate This attribute determines
how the daemon manages path group failback. In this example, the parameter is set to 10 seconds, so failback occurs 10 seconds after a device comes online. To disable the failback, set this parameter to manual. Set it to immediateto force failback to occur immediately.
features "2 pg_init_retries 50" This attribute enables features. In this example, the kernel parameter
pg_init_retriesis set to 50.
The parameter
pg_init_retriesis used to retry the mode select commands.
no_path_retry 30 This attribute determines the
number of retries before queuing is disabled. Set this parameter to fail for immediate failure (no queuing). When this parameter is set to queue, queuing continues indefinitely.
rr_min_io 100 The number of IO to route to
a path before switching to the next in the same path group.
rr_weight priorities If set to priorities the
multipath configurator will assign path weights as "path prio * rr_min_io"