Linux systems

Procedure

Edit the /etc/multipath.conf file to enable multipathing for Linux® hosts.

If the multipath.conf file does not exist, you can create it by issuing the following command:

mpathconf --enable

The following parameters were set in multipath.conf for testing on an IBM® Storwize® system:

defaults {
	     user_friendly_names no
}

devices {
	     device {
		          vendor "IBM "
		          product "2145"
		          path_grouping_policy group_by_prio
		          user_friendly_names no
		          path_selector "round-robin 0"
		          prio "alua"
		          path_checker "tur"
		          failback "immediate"
		          no_path_retry 5
		          rr_weight uniform
		          rr_min_io_rq "1"
		          dev_loss_tmo 120
	    }
}

Set the multipath option to start when the system is started.
Issue the following commands:
```
systemctl enable multipathd.service
systemctl start multipathd.service
```
To verify that disks are visible to the operating system and are managed by multipath, issue the following command:
```
multipath -l
```
Ensure that each device is listed and that it has as many paths as you expect. You can use size and device ID information to identify which disks are listed.
For example, the following output shows that a 2 TB disk has two path groups and four active paths. The 2 TB size confirms that the disk corresponds to a pool file system. Use part of the long device ID number (12, in this example) to search for the volume on the disk-system management interface.
```
[root@tapsrv01 code]# multipath -l
36005076802810c509800000000000012 dm-43 IBM,2145
 size=2.0T features='1 queue_if_no_path' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=0 status=active
| |- 2:0:1:18 sdcw 70:64   active undef running
| `- 4:0:0:18 sdgb 131:112 active undef running
`-+- policy='round-robin 0' prio=0 status=enabled
  |- 1:0:1:18 sdat 66:208  active undef running
  `- 3:0:0:18 sddy 128:0   active undef running
```
1. If needed, correct disk LUN host assignments and force a bus rescan.
  For example:
```
echo "- - -" > /sys/class/scsi_host/host0/scan
echo "- - -" > /sys/class/scsi_host/host1/scan
echo "- - -" > /sys/class/scsi_host/host2/scan
```
  You can also restart the system to rescan disk LUN host assignments.
2. Confirm that disks are now available for multipath I/O by reissuing the multipath -l command.
Use the multipath output to identify and list device IDs for each disk device.

For example, the device ID for your 2 TB disk is 36005076802810c509800000000000012.

Save the list of device IDs to use in the next step.