The software described in this documentation is either in Extended Support or Sustaining Support. See https://www.oracle.com/us/support/library/enterprise-linux-support-policies-069172.pdf for more information.
Oracle recommends that you upgrade the software described by this documentation as soon as possible.
The procedure in this section demonstrates how to set up a simple multipath configuration.
To configure multipathing on a server with access to SAN-attached storage:
Install the
device-mapper-multipath
package:#
yum install device-mapper-multipath
You can now choose one of two configuration paths:
To set up a basic standby failover configuration without editing the
/etc/multipath.conf
configuration file, enter the following command:#
mpathconf --enable --with_multipathd y --with_chkconfig y
This command also starts the
multipathd
service and configures the service to start after system reboots.Skip the remaining steps of this procedure.
To edit
/etc/multipath.conf
and set up a more complex configuration such as active/active, follow the remaining steps in this procedure.
Initialize the
/etc/multipath.conf
file:#
mpathconf --enable
Edit
/etc/multipath.conf
and definedefaults
,blacklist
,blacklist_exceptions
,multipaths
, anddevices
sections as required, for example:defaults { udev_dir /dev polling_interval 10 path_selector "round-robin 0" path_grouping_policy multibus getuid_callout "/lib/udev/scsi_id --whitelisted --device=/dev/%n" prio alua path_checker readsector0 rr_min_io 100 max_fds 8192 rr_weight priorities failback immediate no_path_retry fail user_friendly_names yes } blacklist { # Blacklist by WWID wwid "*" # Blacklist by device name devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*" # Blacklist by device type device { vendor "COMPAQ " product "HSV110 (C)COMPAQ" } } blacklist_exceptions { wwid "3600508b4000156d700012000000b0000" wwid "360000970000292602744533032443941" } multipaths { multipath { wwid 3600508b4000156d700012000000b0000 alias blue path_grouping_policy multibus path_checker readsector0 path_selector "round-robin 0" failback manual rr_weight priorities no_path_retry 5 } multipath { wwid 360000970000292602744533032443941 alias green } } devices { device { vendor "SUN" product "(StorEdge 3510|T4" path_grouping_policy multibus getuid_callout "/sbin/scsi_id --whitelisted --device=/dev/%n" path_selector "round-robin 0" features "0" hardware_handler "0" path_checker directio prio const rr_weight uniform rr_min_io 1000 } }
The sections have the following purposes:
-
defaults
Defines default multipath settings, which can be overridden by settings in the
devices
section, and which in turn can be overridden by settings in themultipaths
section.-
blacklist
Defines devices that are excluded from multipath topology discovery. Blacklisted devices cannot subsumed by a multipath device.
The example shows the three ways that you can use to exclude devices: by WWID (
wwid
), by device name (devnode
), and by device type (device
).-
blacklist_exceptions
Defines devices that are included in multipath topology discovery, even if the devices are implicitly or explicitly listed in the
blacklist
section.-
multipaths
Defines settings for a multipath device that is identified by its WWID.
The
alias
attribute specifies the name of the multipath device as it will appear in/dev/mapper
instead of a name based on either the WWID or the multipath group number.To obtain the WWID of a SCSI device, use the scsi_id command:
#
scsi_id --whitelisted --replace-whitespace --device=
device_name
-
devices
Defines settings for individual types of storage controller. Each controller type is identified by the
vendor
,product
, and optionalrevision
settings, which must match the information insysfs
for the device.You can find details of the storage arrays that DM-Multipath supports and their default configuration values in
/usr/share/doc/device-mapper-multipath-
, which you can use as the basis for entries inversion
/multipath.conf.defaults/etc/multipath.conf
.To add a storage device that DM-Multipath does not list as being supported, obtain the vendor, product, and revision information from the
vendor
,model
, andrev
files under/sys/block/
.device_name
/device
The following entries in
/etc/multipath.conf
would be appropriate for setting up active/passive multipathing to an iSCSI LUN with the specified WWID.defaults { user_friendly_names yes getuid_callout "/bin/scsi_id --whitelisted --replace-whitespace --device=/dev/%n” } multipaths { multipath { wwid 360000970000292602744533030303730 } }
In this standby failover configuration, I/O continues through a remaining active network interface if a network interfaces fails on the iSCSI initiator.
For more information about configuring entries in
/etc/multipath.conf
, refer to themultipath.conf(5)
manual page.-
Start the
multipathd
service and configure the service to start after system reboots:#
service multipathd start
#chkconfig multipathd on
Multipath devices are identified in
/dev/mapper
by their World Wide Identifier
(WWID), which is globally unique. Alternatively, if you set the
value of user_friendly_names
to
yes
in the defaults
section of /etc/multipath.conf
or by
specifying the --user_friendly_names n option
to mpathconf, the device is named
mpath
where
N
N
is the multipath group number. An
alias
attribute in the
multipaths
section of
/etc/multipath.conf
specifies the name of the
multipath device instead of a name based on either the WWID or
the multipath group number.
You can use the multipath device in
/dev/mapper
to reference the storage in the
same way as you would any other physical storage device. For
example, you can configure it as an LVM physical volume, file
system, swap partition, Automatic Storage Management (ASM) disk,
or raw device.
To display the status of DM-Multipath, use the mpathconf command, for example:
# mpathconf
multipath is enabled
find_multipaths is enabled
user_friendly_names is enabled
dm_multipath modules is loaded
multipathd is chkconfiged on
To display the current multipath configuration, specify the -ll option to the multipath command, for example:
# multipath -ll
mpath1(360000970000292602744533030303730) dm-0 SUN,(StorEdge 3510|T4
size=20G features=‘0’ hwhandler=‘0’ wp=rw
|-+- policy=‘round-robin 0’ prio=1 status=active
| ‘- 5:0:0:2 sdb 8:16 active ready running
‘-+- policy=‘round-robin 0’ prio=1 status=active
‘- 5:0:0:3 sdc 8:32 active ready running
In this example, /dev/mapper/mpath1
subsumes
two paths (/dev/sdb
and
/dev/sdc
) to 20 GB of storage in an
active/active configuration using round-robin I/O path
selection. The WWID that identifies the storage is
360000970000292602744533030303730
and the
name of the multipath device under sysfs
is
dm-0
.
If you edit /etc/multipath.conf
, restart the
multipathd
service to make it re-read the
file:
# service multipathd restart
For more information, see the mpathconf(8)
,
multipath(8)
,
multipathd(8)
,
multipath.conf(5)
, and
scsi_id(8)
manual pages.