Before moving on with this section we suggesting reading or being familiar with the topics covered in:
For consistency with those sections, we will refer here to device mapper multipathing as multipath.
Basic setup
Before setting up multipath on your system, ensure that your system has been updated and includes the multipath-tools package. If you want to boot from the storage area network (SAN), then the multipath-tools-boot package is also required.
A very simple /etc/multipath.conf file exists, as explained in the configuration overview. All attributes not declared in multipath.conf are taken from the multipath-tools internal database and its internal blacklist.
The internal attributes database can be acquired by running the following on the command line:
sudo multipath -t
Multipath usually works out-of-the-box with most common storages. This does not mean the default configuration variables should be used in production: the default variables don’t treat important parameters your storage might need.
With the internal attributes (described above), and the example below, you will likely be able to create your /etc/multipath.conf file by squashing the code blocks below. Make sure to read the defaults section attribute comments and make any changes based on what your environment needs.
Example of a defaults section
defaults {
#
# name : polling_interval
# scope : multipathd
# desc : interval between two path checks in seconds. For
# properly functioning paths, the interval between checks
# will gradually increase to (4 * polling_interval).
# values : n > 0
# default : 5
#
polling_interval 10
#
# name : path_selector
# scope : multipath & multipathd
# desc : the default path selector algorithm to use
# these algorithms are offered by the kernel multipath target
# values : "round-robin 0" = Loop through every path in the path group,
# sending the same amount of IO to each.
# "queue-length 0" = Send the next bunch of IO down the path
# with the least amount of outstanding IO.
# "service-time 0" = Choose the path for the next bunch of IO
# based on the amount of outstanding IO to
# the path and its relative throughput.
# default : "service-time 0"
#
path_selector "round-robin 0"
#
# name : path_grouping_policy
# scope : multipath & multipathd
# desc : the default path grouping policy to apply to unspecified
# multipaths
# values : failover = 1 path per priority group
# multibus = all valid paths in 1 priority group
# group_by_serial = 1 priority group per detected serial
# number
# group_by_prio = 1 priority group per path priority
# value
# group_by_node_name = 1 priority group per target node name
# default : failover
#
path_grouping_policy multibus
#
# name : uid_attribute
# scope : multipath & multipathd
# desc : the default udev attribute from which the path
# identifier should be generated.
# default : ID_SERIAL
#
uid_attribute "ID_SERIAL"
#
# name : getuid_callout
# scope : multipath & multipathd
# desc : the default program and args to callout to obtain a unique
# path identifier. This parameter is deprecated.
# This parameter is deprecated, superseded by uid_attribute
# default : /lib/udev/scsi_id --whitelisted --device=/dev/%n
#
getuid_callout "/lib/udev/scsi_id --whitelisted --device=/dev/%n"
#
# name : prio
# scope : multipath & multipathd
# desc : the default function to call to obtain a path
# priority value. The ALUA bits in SPC-3 provide an
# exploitable prio value for example.
# default : const
#
# prio "alua"
#
# name : prio_args
# scope : multipath & multipathd
# desc : The arguments string passed to the prio function
# Most prio functions do not need arguments. The
# datacore prioritizer need one.
# default : (null)
#
# prio_args "timeout=1000 preferredsds=foo"
#
# name : features
# scope : multipath & multipathd
# desc : The default extra features of multipath devices.
# Syntax is "num[ feature_0 feature_1 ...]", where `num' is the
# number of features in the following (possibly empty) list of
# features.
# values : queue_if_no_path = Queue IO if no path is active; consider
# using the `no_path_retry' keyword instead.
# no_partitions = Disable automatic partitions generation via
# kpartx.
# default : "0"
#
features "0"
#features "1 queue_if_no_path"
#features "1 no_partitions"
#features "2 queue_if_no_path no_partitions"
#
# name : path_checker, checker
# scope : multipath & multipathd
# desc : the default method used to determine the paths' state
# values : readsector0|tur|emc_clariion|hp_sw|directio|rdac|cciss_tur
# default : directio
#
path_checker directio
#
# name : rr_min_io
# scope : multipath & multipathd
# desc : the number of IO to route to a path before switching
# to the next in the same path group for the bio-based
# multipath implementation. This parameter is used for
# kernels version up to 2.6.31; newer kernel version
# use the parameter rr_min_io_rq
# default : 1000
#
rr_min_io 100
#
# name : rr_min_io_rq
# scope : multipath & multipathd
# desc : the number of IO to route to a path before switching
# to the next in the same path group for the request-based
# multipath implementation. This parameter is used for
# kernels versions later than 2.6.31.
# default : 1
#
rr_min_io_rq 1
#
# name : flush_on_last_del
# scope : multipathd
# desc : If set to "yes", multipathd will disable queueing when the
# last path to a device has been deleted.
# values : yes|no
# default : no
#
flush_on_last_del yes
#
# name : max_fds
# scope : multipathd
# desc : Sets the maximum number of open file descriptors for the
# multipathd process.
# values : max|n > 0
# default : None
#
max_fds 8192
#
# name : rr_weight
# scope : multipath & multipathd
# desc : if set to priorities the multipath configurator will assign
# path weights as "path prio * rr_min_io"
# values : priorities|uniform
# default : uniform
#
rr_weight priorities
#
# name : failback
# scope : multipathd
# desc : tell the daemon to manage path group failback, or not to.
# 0 means immediate failback, values >0 means deffered
# failback expressed in seconds.
# values : manual|immediate|n > 0
# default : manual
#
failback immediate
#
# name : no_path_retry
# scope : multipath & multipathd
# desc : tell the number of retries until disable queueing, or
# "fail" means immediate failure (no queueing),
# "queue" means never stop queueing
# values : queue|fail|n (>0)
# default : (null)
#
no_path_retry fail
#
# name : queue_without_daemon
# scope : multipathd
# desc : If set to "no", multipathd will disable queueing for all
# devices when it is shut down.
# values : yes|no
# default : yes
queue_without_daemon no
#
# name : user_friendly_names
# scope : multipath & multipathd
# desc : If set to "yes", using the bindings file
# /etc/multipath/bindings to assign a persistent and
# unique alias to the multipath, in the form of mpath<n>.
# If set to "no" use the WWID as the alias. In either case
# this be will be overriden by any specific aliases in this
# file.
# values : yes|no
# default : no
user_friendly_names yes
#
# name : mode
# scope : multipath & multipathd
# desc : The mode to use for the multipath device nodes, in octal.
# values : 0000 - 0777
# default : determined by the process
mode 0644
#
# name : uid
# scope : multipath & multipathd
# desc : The user id to use for the multipath device nodes. You
# may use either the numeric or symbolic uid
# values : <user_id>
# default : determined by the process
uid 0
#
# name : gid
# scope : multipath & multipathd
# desc : The group id to user for the multipath device nodes. You
# may use either the numeric or symbolic gid
# values : <group_id>
# default : determined by the process
gid disk
#
# name : checker_timeout
# scope : multipath & multipathd
# desc : The timeout to use for path checkers and prioritizers
# that issue scsi commands with an explicit timeout, in
# seconds.
# values : n > 0
# default : taken from /sys/block/sd<x>/device/timeout
checker_timeout 60
#
# name : fast_io_fail_tmo
# scope : multipath & multipathd
# desc : The number of seconds the scsi layer will wait after a
# problem has been detected on a FC remote port before failing
# IO to devices on that remote port.
# values : off | n >= 0 (smaller than dev_loss_tmo)
# default : determined by the OS
fast_io_fail_tmo 5
#
# name : dev_loss_tmo
# scope : multipath & multipathd
# desc : The number of seconds the scsi layer will wait after a
# problem has been detected on a FC remote port before
# removing it from the system.
# values : infinity | n > 0
# default : determined by the OS
dev_loss_tmo 120
#
# name : bindings_file
# scope : multipath
# desc : The location of the bindings file that is used with
# the user_friendly_names option.
# values : <full_pathname>
# default : "/var/lib/multipath/bindings"
# bindings_file "/etc/multipath/bindings"
#
# name : wwids_file
# scope : multipath
# desc : The location of the wwids file multipath uses to
# keep track of the created multipath devices.
# values : <full_pathname>
# default : "/var/lib/multipath/wwids"
# wwids_file "/etc/multipath/wwids"
#
# name : reservation_key
# scope : multipath
# desc : Service action reservation key used by mpathpersist.
# values : <key>
# default : (null)
# reservation_key "mpathkey"
#
# name : force_sync
# scope : multipathd
# desc : If set to yes, multipath will run all of the checkers in
# sync mode, even if the checker has an async mode.
# values : yes|no
# default : no
force_sync yes
#
# name : config_dir
# scope : multipath & multipathd
# desc : If not set to an empty string, multipath will search
# this directory alphabetically for files ending in ".conf"
# and it will read configuration information from these
# files, just as if it was in /etc/multipath.conf
# values : "" or a fully qualified pathname
# default : "/etc/multipath/conf.d"
#
# name : delay_watch_checks
# scope : multipathd
# desc : If set to a value greater than 0, multipathd will watch
# paths that have recently become valid for this many
# checks. If they fail again while they are being watched,
# when they next become valid, they will not be used until
# they have stayed up for delay_wait_checks checks.
# values : no|<n> > 0
# default : no
delay_watch_checks 12
#
# name : delay_wait_checks
# scope : multipathd
# desc : If set to a value greater than 0, when a device that has
# recently come back online fails again within
# delay_watch_checks checks, the next time it comes back
# online, it will marked and delayed, and not used until
# it has passed delay_wait_checks checks.
# values : no|<n> > 0
# default : no
delay_wait_checks 12
}
Example of a multipaths section
Note:
You can obtain the WWIDs for your LUNs by running:multipath -ll
after the servicemultipath-tools.servicehas been restarted.
multipaths {
multipath {
wwid 360000000000000000e00000000030001
alias yellow
}
multipath {
wwid 360000000000000000e00000000020001
alias blue
}
multipath {
wwid 360000000000000000e00000000010001
alias red
}
multipath {
wwid 360000000000000000e00000000040001
alias green
}
multipath {
wwid 360000000000000000e00000000050001
alias purple
}
}
Example of a devices section
# devices {
# device {
# vendor "IBM"
# product "2107900"
# path_grouping_policy group_by_serial
# }
# }
#
Example of a blacklist section
# name : blacklist
# scope : multipath & multipathd
# desc : list of device names to discard as not multipath candidates
#
# Devices can be identified by their device node name "devnode",
# their WWID "wwid", or their vender and product strings "device"
# default : fd, hd, md, dm, sr, scd, st, ram, raw, loop, dcssblk
#
# blacklist {
# wwid 26353900f02796769
# devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]\*"
# devnode "^hd[a-z]"
# devnode "^dcssblk[0-9]\*"
# device {
# vendor DEC.\*
# product MSA[15]00
# }
# }
Example of a blacklist exception section
# name : blacklist_exceptions
# scope : multipath & multipathd
# desc : list of device names to be treated as multipath candidates
# even if they are on the blacklist.
#
# Note: blacklist exceptions are only valid in the same class.
# It is not possible to blacklist devices using the devnode keyword
# and to exclude some devices of them using the wwid keyword.
# default : -
#
# blacklist_exceptions {
# devnode "^dasd[c-d]+[0-9]\*"
# wwid "IBM.75000000092461.4d00.34"
# wwid "IBM.75000000092461.4d00.35"
# wwid "IBM.75000000092461.4d00.36"
# }