OS Native Multipathing Software

Configuring the Load Balancing Mode

1. Click the host name and choose Operation > Modify.
   Figure 6-11 Modifying the host properties
   

   The information displayed on the GUI may vary slightly with the product version.

2. Set Host Access Mode to Load balancing for both the local and remote storage systems.
   Figure 6-12 Setting the host access mode
   

Configuring the Local Preferred Mode

1. Click the host name and choose Operation > Modify.
   Figure 6-13 Modifying the host properties
   

   The information displayed on the GUI may vary slightly with the product version.

2. For the local storage system, set Host Access Mode to Asymmetric and Preferred Path for HyperMetro to Yes. For the remote storage system, set Host Access Mode to Asymmetric and Preferred Path for HyperMetro to No.
   Figure 6-14 Settings on the local storage system
   
   Figure 6-15 Settings on the remote storage system
   

Installing Multipathing Software

Generally, multipathing software packages in SUSE are rpm packages starting with device-mapper or multipath-tools, and are installed by default. To install the software manually, upload the software package to the server and use the rpm command to install it. The following is an example.

linux-x8bt:~ # rpm -qa | grep device-mapper*
device-mapper-1.02.149-8.16.x86_64
device-mapper-32bit-1.02.149-8.16.x86_64
linux-x8bt:~ # 
linux-x8bt:~ # rpm -qa | grep multipath*
multipath-tools-0.7.3+102+suse.fb43a08-1.3.x86_64

Modifying the Configuration File

DM-Multipath's most important configuration file is /etc/multipath.conf.

Some operating systems have this file by default. If your operating system does not have this file, you can copy the multipath.conf.synthetic file to the /etc directory to generate one. The following is an example.

linux-x8bt:~ # cp /usr/share/doc/packages/multipath-tools/multipath.conf.synthetic /etc/multipath.conf

If the system does not have a template, run the /sbin/mpathconf --enable command to manually generate /etc/multipath.conf.

If Host Access Mode is set to Load balancing on the storage system, add the following content to the devices field in the /etc/multipath.conf file:

devices {
      device {
               vendor                  "HUAWEI"
               product                 "XSG1"
               path_grouping_policy    multibus
               path_checker            tur
               prio                    const
               path_selector           "round-robin 0"
               failback                immediate
               dev_loss_tmo            30
               fast_io_fail_tmo        5
               no_path_retry           15
}
}

If Host Access Mode is set to Asymmetric on the storage system, add the following content to the devices field in the /etc/multipath.conf file:

devices {
      device {
               vendor                  "HUAWEI"
               product                 "XSG1"
               path_grouping_policy    group_by_prio
               path_checker            tur
               prio                    alua
               path_selector           "round-robin 0"
               failback                immediate
               dev_loss_tmo            30
               fast_io_fail_tmo        5
               no_path_retry           15
}
}

• dev_loss_tmo and fast_io_fail_tmo specify the retry time and switchover time in the event of a link fault. The preceding example provides recommended values for these two parameters, and you can modify them according to your own requirements.
• You are advised to blacklist the WWID of the host's system disk. Otherwise, the system disk may be taken over by multipathing software, resulting in system startup exceptions. For details about how to blacklist WWIDs, see the following link: https://documentation.suse.com/sles/12-SP4/html/SLES-all/cha-multipath.html#sec-multipath-blacklist.
• no_path_retry specifies the retry policy if all paths of a LUN are faulty. The preceding retry time is a recommended value and you can modify it according to your own requirements.
• In SLES 12 SP3, SLES 15, and later versions, due to changes to the kernel parameters, the status displayed by the multipath -ll command may not be updated in the event of a path fault. You are advised to add detect_checker no to the device field.
• After modifying multipath.conf, run /etc/init.d/multipathd restart or systemctl restart multipathd.service to restart the multipath service for the modification to take effect.
• In SLES 12 SP3, SLES 15, and later versions, if blk-mod is used for multi-queue I/O scheduling, I/Os may be suspended for a long time in the event of a fault. You are advised to disable this function. For details, see Modifying the blk-mq Multi-Queue I/O Scheduling Policy

Starting the Multipathing Software

After configuring the configuration file, run the following command on SLES 11 to start the multipath service:

/etc/init.d/multipathd start

For SLES 12 and 15, run the following command to start the multipath service:

systemctl start multipathd.service

Setting the Multipathing Software to Run at System Startup

After enabling the software, you can run the following command on SLES 11 to run the software at system startup:

chkconfig multipathd on

For SLES 12 and 15, run the following command:

systemctl enable multipathd

Rebuilding the Boot Image

For SLES 12 and 15, it is required to rebuild the boot image initrd whenever you enable or disable the multipath service. Otherwise, the system may not boot anymore. When enabling the multipath service, run the following command to rebuild the initrd:

dracut --force --add multipath

When disabling the multipath service, run the following command to rebuild the initrd:

dracut --force -o multipath

Verifying the Load Balancing Mode

Run the multipath -ll command to verify that the configuration has taken effect. In load balancing mode, all paths are active. The following is an example:

[root@localhost ~]# multipath -ll
mpathaf (361603041002d0306003e6dc300000009) dm-9 HUAWEI  ,XSG1            
size=5.0G features='0' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
  |- 2:0:2:4 sde  8:64   active ready running
  |- 9:0:2:4 sdq  65:0   active ready running
  |- 2:0:3:4 sdaw 67:0   active ready running
  |- 9:0:3:4 sdas 66:192 active ready running
  |- 2:0:0:4 sdi  8:128  active ready running
  |- 9:0:0:4 sdak 66:64  active ready running
  |- 2:0:1:4 sdo  8:224  active ready running
  `- 9:0:1:4 sdao 66:128 active ready running
mpathae (361603041002d0306003e549f00000000) dm-3 HUAWEI  ,XSG1            
size=50G features='0' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
  |- 2:0:2:1 sdb  8:16   active ready running
  |- 9:0:2:1 sdm  8:192  active ready running
  |- 2:0:3:1 sdat 66:208 active ready running
  |- 9:0:3:1 sdap 66:144 active ready running
  |- 2:0:0:1 sdf  8:80   active ready running
  |- 9:0:0:1 sdah 66:16  active ready running
  |- 2:0:1:1 sdj  8:144  active ready running
  `- 9:0:1:1 sdal 66:80  active ready running

Verifying the Local Preferred Mode

Run the multipath -ll command to verify that the configuration has taken effect. In local preferred mode, status=active corresponds to the preferred paths on the local storage system, and status=enabled corresponds to the non-preferred paths on the remote storage system. The following command output indicates that the configuration has taken effect. Generally, the prio value of preferred paths is 50 and that of non-preferred paths is 10 in Linux systems. The following is an example:

[root@localhost ~]# multipath -ll
mpathaf (361603041002d0306003e6dc300000009) dm-9 HUAWEI  ,XSG1            
size=5.0G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=50 status=active
| |- 2:0:2:4 sdak 66:64  active ready running
| |- 9:0:2:4 sdba 67:64  active ready running
| |- 2:0:3:4 sdao 66:128 active ready running
| |- 9:0:3:4 sdbe 67:128 active ready running
`-+- policy='round-robin 0' prio=10 status=enabled
  |- 2:0:0:4 sdh  8:112  active ready running
  |- 9:0:0:4 sdi  8:128  active ready running
  |- 2:0:1:4 sdp  8:240  active ready running
  |- 9:0:1:4 sdq  65:0   active ready running