4.10. Modifying multipath settings for storage controllers

Procedure

1. View the information about the default configuration value, including supported devices:

   # multipathd show config
   # multipath -t

   Many devices that support multipathing are included by default in a multipath configuration.

2. Optional: If you need to modify the default configuration values, you can overwrite the default values by including an entry in the configuration file for the device that overwrites those values. You can copy the device configuration defaults for the device that the multipathd show config command displays and override the values that you want to change.

3. Add a device that is not configured automatically by default to the devices section of the configuration file by setting the vendor and product parameters. Find these values by opening the /sys/block/device_name/device/vendor and /sys/block/device_name/device/model files where device_name is the device to be multipathed, as mentioned in the following example:

   # cat /sys/block/sda/device/vendor
   WINSYS
   # cat /sys/block/sda/device/model
   SF2372

4. Optional: Specify the additional parameters depending on your specific device:

   active/active device

   Usually there is no need to set additional parameters in this case. If required, you might set path_grouping_policy to multibus. Other parameters you may need to set are no_path_retry and rr_min_io.

   active/passive device

   If it automatically switches paths with I/O to the passive path, you need to change the checker function to one that does not send I/O to the path to test if it is working, otherwise, your device will keep failing over. This means that you have set the path_checker to tur, which works for all SCSI devices that support the Test Unit Ready command, which most do.

   If the device needs a special command to switch paths, then configuring this device for multipath requires a hardware handler kernel module. The current available hardware handler is emc. If this is not sufficient for your device, you might not be able to configure the device for multipath.

   The following example shows a device entry in the multipath configuration file:

   #	}
   #	device {
   #		vendor			"COMPAQ  "
   #		product			"MSA1000         "
   #		path_grouping_policy	multibus
   #		path_checker		tur
   #		rr_weight		priorities
   #	}
   #}

5. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

   • To display any configuration errors, run:

     # multipath -t > /dev/null

   • To display the new configuration with the changes added, run:

     # multipath -t

6. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:

   # service multipathd reload