overview of multipath
Without DM Multipath, each path from a server node to a storage controller is treated by the system as a separate device, even when the I/O path connects the same server node to the same storage controller. DM Multipath provides a way of organizing the I/O paths logically, by creating a single multipath device on top of the underlying devices.
To make multipath work make sure below module is loaded
dm_multipath 27427 4 dm_round_robin,dm_service_time
filename: /lib/modules/3.10.0-693.21.1.el7.x86_64/kernel/drivers/md/dm-multipath.ko.xz
license: GPL
author: Sistina Software <dm-devel@redhat.com>
description: device-mapper multipath target
retpoline: Y
rhelversion: 7.4
srcversion: 063067F9F167E7B653A4773
depends: dm-mod
intree: Y
vermagic: 3.10.0-693.21.1.el7.x86_64 SMP mod_unload modversions
signer: Red Hat Enterprise Linux kernel signing key
sig_key: B1:C3:31:09:FB:DA:94:AD:2F:E1:E8:E5:C1:E5:52:BD:22:57:60:FE
sig_hashalgo: sha256
Below is the main device mapper rpm
device-mapper
Main configuration file
Viewing the connected and scanned multipath devices
Get the WWID of the connected/scanned LUN
Each multipath device has a World Wide Identifier (WWID), which is guaranteed to be globally unique and unchanging.
You can get the WWID using below commands
3600c0ff00013b88f9058e35a01000000 dm-0 HP ,P2000 G3 FC
3600c0ff00013b88f9c58e35a01000000 dm-6 HP ,P2000 G3 FC
OR using below command
lrwxrwxrwx 1 root root 9 May 22 18:29 /dev/disk/by-id/scsi-3600c0ff00013b88f9058e35a01000000 -> ../../sde
lrwxrwxrwx 1 root root 9 May 22 18:29 /dev/disk/by-id/scsi-3600c0ff00013b88f9c58e35a01000000 -> ../../sdd
Get the WWID of the disks
[0:0:0:0] disk HP P2000 G3 FC T252 /dev/sda 3600c0ff00013b88f9058e35a01000000
[0:0:0:1] disk HP P2000 G3 FC T252 /dev/sdb 3600c0ff00013b88f9c58e35a01000000
[0:0:1:0] disk HP P2000 G3 FC T252 /dev/sdc 3600c0ff00013b88f9058e35a01000000
[0:0:1:1] disk HP P2000 G3 FC T252 /dev/sdd 3600c0ff00013b88f9c58e35a01000000
[1:0:0:0] disk HP P2000 G3 FC T252 /dev/sde 3600c0ff00013b88f9058e35a01000000
[1:0:0:1] disk HP P2000 G3 FC T252 /dev/sdf 3600c0ff00013b88f9c58e35a01000000
[1:0:1:0] disk HP P2000 G3 FC T252 /dev/sdg 3600c0ff00013b88f9058e35a01000000
[1:0:1:1] disk HP P2000 G3 FC T252 /dev/sdh 3600c0ff00013b88f9c58e35a01000000
To get the WWID of the disks you can also use below command
3600c0ff00013b88f9058e35a01000000
Get the list of disks mapped via HBA to the Linux box
A node with two HBAs attached to a storage controller with two ports by means of a single unzoned FC switch sees four devices: /dev/sda, /dev/sdb, dev/sdc, and /dev/sdd. DM Multipath creates a single device with a unique WWID that reroutes I/O to those four underlying devices according to the multipath configuration.
For our case since we have two LUNs connected to the Linux box hence we see 8 devices
lrwxrwxrwx 1 root root 0 May 22 18:29 /sys/block/sda/device -> ../../../0:0:0:0
lrwxrwxrwx 1 root root 0 May 22 18:29 /sys/block/sdb/device -> ../../../0:0:0:1
lrwxrwxrwx 1 root root 0 May 22 18:29 /sys/block/sdc/device -> ../../../0:0:1:0
lrwxrwxrwx 1 root root 0 May 22 18:29 /sys/block/sdd/device -> ../../../0:0:1:1
lrwxrwxrwx 1 root root 0 May 22 18:29 /sys/block/sde/device -> ../../../1:0:0:0
lrwxrwxrwx 1 root root 0 May 22 18:29 /sys/block/sdf/device -> ../../../1:0:0:1
lrwxrwxrwx 1 root root 0 May 22 18:29 /sys/block/sdg/device -> ../../../1:0:1:0
lrwxrwxrwx 1 root root 0 May 22 18:29 /sys/block/sdh/device -> ../../../1:0:1:1
The same can be seen via below command where LUN to device mapping does easier on the eyes
total 0
lrwxrwxrwx 1 root root 9 May 22 18:29 pci-0000:04:00.2-fc-0x207000c0ff13d3a7-lun-0 -> ../../sda
lrwxrwxrwx 1 root root 9 May 22 18:29 pci-0000:04:00.2-fc-0x207000c0ff13d3a7-lun-1 -> ../../sdb
lrwxrwxrwx 1 root root 9 May 22 18:29 pci-0000:04:00.2-fc-0x247000c0ff13d3a7-lun-0 -> ../../sdc
lrwxrwxrwx 1 root root 9 May 22 18:29 pci-0000:04:00.2-fc-0x247000c0ff13d3a7-lun-1 -> ../../sdd
lrwxrwxrwx 1 root root 9 May 22 18:29 pci-0000:04:00.3-fc-0x217000c0ff13d3a7-lun-0 -> ../../sdg
lrwxrwxrwx 1 root root 9 May 22 18:29 pci-0000:04:00.3-fc-0x217000c0ff13d3a7-lun-1 -> ../../sdh
lrwxrwxrwx 1 root root 9 May 22 18:29 pci-0000:04:00.3-fc-0x257000c0ff13d3a7-lun-0 -> ../../sde
lrwxrwxrwx 1 root root 9 May 22 18:29 pci-0000:04:00.3-fc-0x257000c0ff13d3a7-lun-1 -> ../../sdf
Understanding the Device ID
In multipath output we see below highlighted entry being used (and also in the commands above you would see similar representation)
3600c0ff00013b88f9058e35a01000000 dm-0 HP ,P2000 G3 FC
size=102G features='1 queue_if_no_path' hwhandler='0' wp=rw
|-+- policy='service-time 0' prio=0 status=active
| |- 0:0:0:0 sda 8:0 active undef unknown
| `- 1:0:1:0 sdg 8:96 active undef unknown
`-+- policy='service-time 0' prio=0 status=enabled
|- 0:0:1:0 sdc 8:32 active undef unknown
`- 1:0:0:0 sde 8:64 active undef unknown
3600c0ff00013b88f9c58e35a01000000 dm-6 HP ,P2000 G3 FC
size=359G features='1 queue_if_no_path' hwhandler='0' wp=rw
|-+- policy='service-time 0' prio=0 status=active
| |- 0:0:0:1 sdb 8:16 active undef unknown
| `- 1:0:1:1 sdh 8:112 active undef unknown
`-+- policy='service-time 0' prio=0 status=enabled
|- 0:0:1:1 sdd 8:48 active undef unknown
`- 1:0:0:1 sdf 8:80 active undef unknown
Below value explains what each field means
^ ^ ^ ^
| | | |
H C T L
Where H is the HBA number, C is the channel on the HBA, T is the SCSI target ID, and L is the LUN from the Storage.
Flush/Remove all the multipath device
Flush/Remove selected multipath device.
First of all the the WWID of the multipath device which you want to flush using multipath -ll
3600c0ff00013b88fdc53e35a01000000 dm-0 HP ,P2000 G3 FC
size=186G features='1 queue_if_no_path' hwhandler='0' wp=rw
|-+- policy='service-time 0' prio=50 status=active
| |- 1:0:0:0 sda 8:0 active ready running
| `- 2:0:1:0 sdd 8:48 active ready running
`-+- policy='service-time 0' prio=10 status=enabled
|- 1:0:1:0 sdb 8:16 active ready running
`- 2:0:0:0 sdc 8:32 active ready running
Next flush the selected multipath using below command
NOTE: This multipath must not be in used state
Show the existing configuration in detail
defaults {
verbosity 2
polling_interval 5
max_polling_interval 20
reassign_maps "yes"
multipath_dir "/lib64/multipath"
path_selector "service-time 0"
path_grouping_policy "failover"
uid_attribute "ID_SERIAL"
prio "const"
prio_args ""
features "0"
path_checker "directio"
alias_prefix "mpath"
failback "immediate"
rr_min_io 1000
rr_min_io_rq 1
max_fds 1048576
rr_weight "uniform"
queue_without_daemon "no"
flush_on_last_del "no"
user_friendly_names "no"
fast_io_fail_tmo 5
bindings_file "/etc/multipath/bindings"
wwids_file /etc/multipath/wwids
prkeys_file /etc/multipath/prkeys
log_checker_err always
find_multipaths no
retain_attached_hw_handler no
detect_prio no
detect_path_checker no
hw_str_match no
force_sync no
deferred_remove no
ignore_new_boot_devs no
skip_kpartx no
config_dir "/etc/multipath/conf.d"
delay_watch_checks no
delay_wait_checks no
retrigger_tries 3
retrigger_delay 10
missing_uev_wait_timeout 30
new_bindings_in_boot no
remove_retries 0
disable_changed_wwids no
unpriv_sgio no
}
blacklist {
devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
devnode "^hd[a-z][[0-9]*]"
devnode "^cciss!c[0-9]d[0-9]*[p[0-9]*]"
devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
devnode "^(td|hd|vd)[a-z]"
devnode "^dcssblk[0-9]*"
device {
vendor "DGC"
product "LUNZ"
}
device {
vendor "EMC"
product "LUNZ"
}
device {
vendor "IBM"
product "Universal Xport"
}
device {
vendor "IBM"
product "S/390.*"
}
device {
vendor "DELL"
product "Universal Xport"
}
device {
vendor "SGI"
product "Universal Xport"
}
device {
vendor "STK"
product "Universal Xport"
}
device {
vendor "SUN"
product "Universal Xport"
}
device {
vendor "(NETAPP|LSI|ENGENIO)"
product "Universal Xport"
}
}
blacklist_exceptions {
}
devices {
device {
vendor "HP"
product "MSA2012sa|MSA23(12|24)(fc|i|sa)|MSA2000s VOLUME"
path_grouping_policy "group_by_prio"
path_checker "tur"
features "0"
hardware_handler "0"
prio "alua"
failback immediate
rr_weight "uniform"
no_path_retry 18
rr_min_io 100
}
device {
vendor "HP"
product "MSA (1|2)040 SA(N|S)"
path_grouping_policy "group_by_prio"
path_checker "tur"
features "0"
hardware_handler "0"
prio "alua"
failback immediate
rr_weight "uniform"
no_path_retry 18
rr_min_io 100
}
device {
vendor "HP"
product "HSVX700"
path_grouping_policy "group_by_prio"
path_checker "tur"
features "0"
hardware_handler "1 alua"
prio "alua"
failback immediate
rr_weight "uniform"
no_path_retry 12
rr_min_io 100
}
device {
vendor "HP"
product "LOGICAL VOLUME.*"
path_grouping_policy "multibus"
path_checker "tur"
features "0"
hardware_handler "0"
prio "const"
rr_weight "uniform"
no_path_retry 12
}
device {
vendor "HP"
product "P2000 G3 FC|P2000G3 FC/iSCSI|P2000 G3 SAS|P2000 G3 iSCSI"
path_grouping_policy "group_by_prio"
path_checker "tur"
features "0"
hardware_handler "0"
prio "alua"
failback immediate
rr_weight "uniform"
no_path_retry 18
rr_min_io 100
}
device {
vendor "IBM"
product "^1722-600"
product_blacklist "Universal Xport"
path_grouping_policy "group_by_prio"
path_checker "rdac"
features "1 queue_if_no_path"
hardware_handler "1 rdac"
prio "rdac"
failback immediate
rr_weight "uniform"
no_path_retry 300
}
device {
vendor "IBM"
product "^1724"
product_blacklist "Universal Xport"
path_grouping_policy "group_by_prio"
path_checker "rdac"
features "1 queue_if_no_path"
hardware_handler "1 rdac"
prio "rdac"
failback immediate
rr_weight "uniform"
no_path_retry 300
}
device {
vendor "IBM"
product "^1726"
product_blacklist "Universal Xport"
path_grouping_policy "group_by_prio"
path_checker "rdac"
features "1 queue_if_no_path"
hardware_handler "1 rdac"
prio "rdac"
failback immediate
rr_weight "uniform"
no_path_retry 300
}
device {
vendor "IBM"
product "^1742"
product_blacklist "Universal Xport"
path_grouping_policy "group_by_prio"
path_checker "rdac"
features "0"
hardware_handler "1 rdac"
prio "rdac"
failback immediate
rr_weight "uniform"
no_path_retry "queue"
}
device {
vendor "IBM"
product "^1745|^1746"
product_blacklist "Universal Xport"
path_grouping_policy "group_by_prio"
path_checker "rdac"
features "2 pg_init_retries 50"
hardware_handler "1 rdac"
prio "rdac"
failback immediate
rr_weight "uniform"
no_path_retry 15
}
device {
vendor "IBM"
product "^1814"
product_blacklist "Universal Xport"
path_grouping_policy "group_by_prio"
path_checker "rdac"
features "0"
hardware_handler "1 rdac"
prio "rdac"
failback immediate
rr_weight "uniform"
no_path_retry "queue"
}
device {
vendor "IBM"
product "^1815"
product_blacklist "Universal Xport"
path_grouping_policy "group_by_prio"
path_checker "rdac"
features "0"
hardware_handler "1 rdac"
prio "rdac"
failback immediate
rr_weight "uniform"
no_path_retry "queue"
}
device {
vendor "IBM"
product "^1818"
product_blacklist "Universal Xport"
path_grouping_policy "group_by_prio"
path_checker "rdac"
features "0"
hardware_handler "1 rdac"
prio "rdac"
failback immediate
rr_weight "uniform"
no_path_retry "queue"
}
device {
vendor "IBM"
product "^3526"
product_blacklist "Universal Xport"
path_grouping_policy "group_by_prio"
path_checker "rdac"
features "0"
hardware_handler "1 rdac"
prio "rdac"
failback immediate
rr_weight "uniform"
no_path_retry "queue"
}
device {
vendor "IBM"
product "^3542"
path_grouping_policy "group_by_serial"
path_checker "tur"
features "0"
hardware_handler "0"
prio "const"
rr_weight "uniform"
}
device {
vendor "IBM"
product "^2105800"
path_grouping_policy "group_by_serial"
path_checker "tur"
features "1 queue_if_no_path"
hardware_handler "0"
prio "const"
rr_weight "uniform"
}
device {
vendor "IBM"
product "2810XIV"
path_grouping_policy "multibus"
path_checker "tur"
features "1 queue_if_no_path"
hardware_handler "0"
prio "const"
failback 15
rr_weight "uniform"
rr_min_io 15
}
device {
vendor "AIX"
product "VDASD"
path_grouping_policy "multibus"
path_checker "directio"
features "0"
hardware_handler "0"
prio "const"
failback immediate
rr_weight "uniform"
no_path_retry 60
}
device {
vendor "PURE"
product "FlashArray"
path_grouping_policy "multibus"
path_selector "queue-length 0"
path_checker "tur"
features "0"
hardware_handler "0"
prio "const"
failback immediate
fast_io_fail_tmo 10
dev_loss_tmo 60
user_friendly_names no
}
device {
vendor "HUAWEI"
product "XSG1"
path_grouping_policy "multibus"
path_checker "tur"
features "0"
hardware_handler "0"
failback immediate
}
device {
vendor "Ceph"
product "RBD"
path_grouping_policy "failover"
path_checker "rbd"
no_path_retry "fail"
}
}
multipaths {
}
Get complete HBA details
systool uses APIs provided by libsysfs to gather information and will give detailed information about the available HBA and the LUN status
NOTE: systool is delivered with sysfsutils rpm so make sure it is installed before using this tool
Class = "fc_host"
Class Device = "host0"
Class Device path = "/sys/devices/pci0000:00/0000:00:02.0/0000:04:00.2/host0/fc_host/host0"
active_fc4s = "0x00 0x00 0x01 0x00 0x00 0x00 0x00 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 "
dev_loss_tmo = "30"
fabric_name = "0x2003547fee1188d9"
issue_lip = <store method only>
max_npiv_vports = "255"
maxframe_size = "2048 bytes"
node_name = "0x50060b0000c2a67d"
npiv_vports_inuse = "0"
port_id = "0x310305"
port_name = "0x50060b0000c2a67c"
port_state = "Online"
port_type = "NPort (fabric via point-to-point)"
speed = "unknown"
supported_classes = "Class 3"
supported_fc4s = "0x00 0x00 0x01 0x00 0x00 0x00 0x00 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 "
supported_speeds = "10 Gbit"
symbolic_name = "Emulex 554FLB FV11.1.183.23 DV11.2.0.6 HN:ban33-be002-2b OS:Linux"
tgtid_bind_type = "wwpn (World Wide Port Name)"
uevent =
vport_create = <store method only>
vport_delete = <store method only>
Device = "host0"
Device path = "/sys/devices/pci0000:00/0000:00:02.0/0000:04:00.2/host0"
uevent = "DEVTYPE=scsi_host"
Class Device = "host1"
Class Device path = "/sys/devices/pci0000:00/0000:00:02.0/0000:04:00.3/host1/fc_host/host1"
active_fc4s = "0x00 0x00 0x01 0x00 0x00 0x00 0x00 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 "
dev_loss_tmo = "30"
fabric_name = "0x2003547fee357a81"
issue_lip = <store method only>
max_npiv_vports = "255"
maxframe_size = "2048 bytes"
node_name = "0x50060b0000c2a67f"
npiv_vports_inuse = "0"
port_id = "0x25030f"
port_name = "0x50060b0000c2a67e"
port_state = "Online"
port_type = "NPort (fabric via point-to-point)"
speed = "unknown"
supported_classes = "Class 3"
supported_fc4s = "0x00 0x00 0x01 0x00 0x00 0x00 0x00 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 "
supported_speeds = "10 Gbit"
symbolic_name = "Emulex 554FLB FV11.1.183.23 DV11.2.0.6 HN:ban33-be002-2b OS:Linux"
tgtid_bind_type = "wwpn (World Wide Port Name)"
uevent =
vport_create = <store method only>
vport_delete = <store method only>
Device = "host1"
Device path = "/sys/devices/pci0000:00/0000:00:02.0/0000:04:00.3/host1"
uevent = "DEVTYPE=scsi_host"
This tool can also be used to get other values using below syntax
To get the port name
Class = "fc_host"
Class Device = "host0"
port_name = "0x50060b0000c2a67c"
Device = "host0"
Class Device = "host1"
port_name = "0x50060b0000c2a67e"
Device = "host1"
To get the port id
Class = "fc_host"
Class Device = "host0"
port_id = "0x310305"
Device = "host0"
Class Device = "host1"
port_id = "0x25030f"
Device = "host1"
Show the existing configuration in brief
multipath is enabled
find_multipaths is disabled
user_friendly_names is enabled
dm_multipath module is loaded
multipathd is running
Using user friendly names for multipath
Each multipath device has a World Wide Identifier (WWID), which is guaranteed to be globally unique and unchanging. By default, the name of a multipath device is set to its WWID. Alternately, you can set the user_friendly_names option in the multipath configuration file, which sets the alias to a nodeunique name of the form mpathn
With user_friendly name disabled we will only see the WWID of the multipath connected
3600c0ff000144876f85ae35a01000000 dm-0 HP ,P2000 G3 FC
size=102G features='1 queue_if_no_path' hwhandler='0' wp=rw
|-+- policy='service-time 0' prio=0 status=active
| `- 2:0:0:0 sda 8:0 active undef unknown
`-+- policy='service-time 0' prio=0 status=enabled
`- 2:0:1:0 sdc 8:32 active undef unknown
3600c0ff000144876065be35a01000000 dm-6 HP ,P2000 G3 FC
size=359G features='1 queue_if_no_path' hwhandler='0' wp=rw
|-+- policy='service-time 0' prio=0 status=active
| `- 2:0:0:1 sdb 8:16 active undef unknown
`-+- policy='service-time 0' prio=0 status=enabled
`- 2:0:1:1 sdd 8:48 active undef unknown
Next enable user_friendly name
Check the multipath
mpathb (3600c0ff000144876065be35a01000000) dm-6 HP ,P2000 G3 FC
size=359G features='1 queue_if_no_path' hwhandler='0' wp=rw
|-+- policy='service-time 0' prio=0 status=active
| `- 2:0:0:1 sdb 8:16 active undef unknown
`-+- policy='service-time 0' prio=0 status=enabled
`- 2:0:1:1 sdd 8:48 active undef unknown
mpatha (3600c0ff000144876f85ae35a01000000) dm-0 HP ,P2000 G3 FC
size=102G features='1 queue_if_no_path' hwhandler='0' wp=rw
|-+- policy='service-time 0' prio=0 status=active
| `- 2:0:0:0 sda 8:0 active undef unknown
`-+- policy='service-time 0' prio=0 status=enabled
`- 2:0:1:0 sdc 8:32 active undef unknown
The mapping is done using /etc/multipath/bindings.
Check the number of HBA on your Linux box
total 0
lrwxrwxrwx 1 root root 0 May 22 18:29 host0 -> ../../devices/pci0000:00/0000:00:02.0/0000:04:00.2/host0/fc_host/host0
lrwxrwxrwx 1 root root 0 May 22 18:29 host1 -> ../../devices/pci0000:00/0000:00:02.0/0000:04:00.3/host1/fc_host/host1
You can also check the same using
04:00.2 Fibre Channel [0c04]: Emulex Corporation OneConnect 10Gb FCoE Initiator (be3) [19a2:0714] (rev 01)
04:00.3 Fibre Channel [0c04]: Emulex Corporation OneConnect 10Gb FCoE Initiator (be3) [19a2:0714] (rev 01)
On some Linux variant you can also grep for HBA
So here I have two HBA
Check the WWPN of the multipath
A worldwide port number (WWPN) is unique identifier for each FC port of any Fibre Channel device.
- For server, we have a WWPN for each port of the HBA.
- For a SAN switch, the WWPN is available for each port in the chassis.
- For Storage, each host port has an individual WWPN
Here we have two HBA so each HBA will have unique World Wide Port Name (WWPN) which will be connected to the SAN switch then to the Storage Box.
From my Linux Box
0x50060b0000c2a67c
# cat /sys/class/fc_host/host1/port_name
0x50060b0000c2a67e
These are the WWPN number.
Check the WWNN of the multipath
A worldwide node name (WWNN) is a globally unique 64-bit identifier that is assigned to each Fibre Channel node or device.
- For servers and hosts, WWNN is unique for each HBA (host bus adapter), and in a case of a server with two HBAs, they have two WWNNs.
- For a SAN switch, the WWNN is a common for the chassis.
- For storage, the WWNN is common for each controller unit of midrage storage
Since here I have two HBA hence there are two WWNN for each HBA
From my Linux Box
0x50060b0000c2a67f
# cat /sys/class/fc_host/host0/node_name
0x50060b0000c2a67d
Perform rescan of the connected HBA for new LUNs
If you have new LUNs connected to your Linux box then you will need to rescan the HBA
Assuming you know the WWPN for which the new LUN was added
# systemctl reload multipathd
# multipath -v2
Next validate if the new LUN is visible using
Blacklist a device
Create a function like below in /etc/multipath.conf where you can give the list of devices which you wish to blacklist
Here I am blacklisting multiple devices which I do not wish to be created as multipath
devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
devnode "^hd[a-z][[0-9]*]"
devnode "^cciss!c[0-9]d[0-9]*[p[0-9]*]"
}
To blacklist using WWID
You can get the WWID of a device using below command
3600c0ff000144876f85ae35a01000000
Here we are blacklisting /dev/sda which is our internal disk and I donot want it to be a multipath
wwid 3600c0ff000144876f85ae35a01000000
}
Perform a multipathd reload to take the changes affect
Add blacklist exception for selected disks
Similar to blacklisting we can also add a blacklist exception so that these devices are not blacklisted
Add below function in /etc/multipath.conf with the list of wwid which you wish to add as an exception for blacklist
wwid "3600d0230000000000e13955cc3757803"
}
Followed by reload of multipathd
Change configuration (path selector) of the multipath device
Below is the total list of supported path_selector
Add your choice of path_selector in /etc/multipath.conf as shown below
user_friendly_names yes
failback immediate
path_selector "round-robin 0"
}
Either you add it under defaults function or you can add a device function if you wish to add to change path selector only for a selected device
device {
vendor "HP"
product "P2000 G3 FC|P2000G3 FC/iSCSI|P2000 G3 SAS|P2000 G3 iSCSI"
path_grouping_policy "failover"
path_selector "round-robin 0"
}
}
NOTE: You can get the device detail from "multipathd show config"
Add below changes
device {
vendor "HP"
product "P2000 G3 FC|P2000G3 FC/iSCSI|P2000 G3 SAS|P2000 G3 iSCSI"
user_friendly_names yes
}
}
I hope the article was useful.