The multipath.conf files blacklists EVERYTHING by default. So ensure the first lines are commented out

blacklist {
        devnode "*"
}

After commenting out the general blacklist you can then specify general types of devices to black list or even individual devices.

This can be done in 3 ways:

Using WWID This blocks the device with wwid = 99999999999999999

blacklist {
       wwid 99999999999999999
}

Using Device nodes You can also block out all devices of certain types for example: Blocking all SCSI devices:

blacklist {
       devnode "^sd[a-z]"
}

Using Device Types The following example blacklists all IBM DS4200 device and all HP devices.

blacklist {
       device {
               vendor  "IBM"
               product "3S42"       #DS4200 Product 10
       }
       device {
               vendor  "HP"
               product "*"
       }
}