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4.2. Configuration File Blacklist

The blacklist section of the multipath configuration file specifies the devices that will not be used when the system configures multipath devices. Devices that are blacklisted will not be grouped into a multipath device.
By default, all devices are blacklisted, since the following lines appear in the initial configuration file. 
blacklist {
        devnode "*"
}
To enable multipathing on all of the devices that are supported by default, comment out those lines, as described in Section 3.1, “Setting Up DM-Multipath”.
After commenting out the universal blacklist, you can specify general device types and individual devices to blacklist. You can blacklist devices according to the following criteria:
By default, a variety of device types are blacklisted, even after you comment out the initial blacklist section of the configuration file. For information, see Section 4.2.2, “Blacklisting By Device Name”.

4.2.1. Blacklisting by WWID

You can specify individual devices to blacklist by their World-Wide IDentification with a wwid entry in the blacklist section of the configuration file.
The following example shows the lines in the configuration file that would blacklist a device with a WWID of 26353900f02796769. 
blacklist {
       wwid 26353900f02796769
}

4.2.2. Blacklisting By Device Name

You can blacklist device types by device name so that they will not be grouped into a multipath device by specifying a devnode entry in the blacklist section of the configuration file.
The following example shows the lines in the configuration file that would blacklist all SCSI devices, since it blacklists all sd* devices. 
blacklist {
       devnode "^sd[a-z]"
}
You can use a devnode entry in the blacklist section of the configuration file to specify individual devices to blacklist rather than all devices of specific type; this is not recommended, however. Unless it is statically mapped by udev rules, there is no guarantee that a specific device will have the same name on reboot. For example, a device name could change from /dev/sda to /dev/sdb on reboot.
By default, the following devnode entries are compiled in the default blacklist; the devices that these entries blacklist do not generally support DM-Multipath. To enable multipathing on any of these devices, you would need to specify them in the blacklist_exceptions section of the configuration file, as described in Section 4.2.4, “Blacklist Exceptions”. 
blacklist {
       devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
       devnode "^hd[a-z]"
}

4.2.3. Blacklisting By Device Type

You can specify specific device types in the blacklist section of the configuration file with a device section. The following example blacklists all IBM DS4200 and HP devices. 
blacklist {
       device {
               vendor  "IBM"
               product "3S42"       #DS4200 Product 10
       }
       device {
               vendor  "HP"
               product "*"
       }
}

4.2.4. Blacklist Exceptions

You can use the blacklist_exceptions section of the configuration file to enable multipathing on devices that have been blacklisted by default. For example, by default, devices with vendor = "IBM" and product = "S/390.*" are blacklisted since usually DASD devices are used for local storage. If you do need to enable multipathing on these devices, uncomment the following lines in the configuration file: 
blacklist_exceptions {
       device {
               vendor  "IBM"
               product "S/390.*"
       }
}
When specifying devices in the blacklist_exceptions section of the configuration file, you must specify the exceptions in the same way they were specified in the blacklist. For example, a WWID exception will not apply to devices specified by a devnode blacklist entry, even if the blacklisted device is associated with that WWID. Similarly, devnode exceptions apply only to devnode entries, and device exceptions apply only to device entries.