5.8. Adding exceptions for devices with disabled multipathing

Procedure

1. Enable multipathing on the devices by using the blacklist_exceptions section of the /etc/multipath.conf configuration file.

   When specifying devices in the blacklist_exceptions section of the configuration file, you must specify the exceptions by using the same criteria as they were specified in the blacklist section. For example, a WWID exception does not apply to devices disabled by a devnode entry, even if the disabled device is associated with that WWID. Similarly, devnode exceptions apply only to devnode entries, and device exceptions apply only to device entries.

   Following is an example for adding exceptions for devices with disabled multipathing

   • An exception by WWID

     If you have a large number of devices and want to multipath only one of them with the WWID of 3600d0230000000000e13955cc3757803, instead of individually disabling each of the devices except the one you want, you could disable all of them, and then enable only the one you want by adding the following lines to the /etc/multipath.conf file:

     blacklist {
             wwid ".*"
     }
     
     blacklist_exceptions {
             wwid "3600d0230000000000e13955cc3757803"
     }

     Alternatively, you could use an exclamation mark (!) to invert the blacklist entry, which disables all devices except the specified WWID:

     blacklist {
             wwid "!3600d0230000000000e13955cc3757803"
     }

   • An exception by udev property

     The property parameter works differently than the other blacklist_exception parameters. The value of the property parameter must match the name of a variable in the udev database. Otherwise, the device is disabled. Using this parameter, you can disable multipathing on certain SCSI devices, such as USB sticks and local hard drives.

     To enable multipathing only on SCSI devices that could reasonably be multipathed, set this parameter to (SCSI_IDENT_|ID_WWN) as in the following example:

     blacklist_exceptions {
             property "(SCSI_IDENT_|ID_WWN)"
     }

2. 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

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

   # service multipathd reload