5.6. Resizing an Online Multipathed Device (RHEL 4.8 and later)

In systems running RHEL 4.8 and later, is is possible to resize a multipath device while it is online. This allows you to resize the device when it is open, as when a file system is currently mounted.
Use the following procedure to resize an online multipath device.
  1. Resize your physical device.
  2. Resize your paths. For SCSI devices, writing a 1 to the rescan file for the device causes the SCSI driver to rescan. You can use the following command: 
    # echo 1 > /sys/block/device_name/device/rescan
  3. Resize your multipath device by running the multipath command: 
    #  multipath
Your hardware setup may require that you temporarily take the actual storage offline in order to resize your physical device. If you take your storage offline and your multipath device is not set to queue when all paths are down, any I/O activity while your storage is offline will fail. You can work around this by executing the following command before taking your storage offline: 
#  dmsetup suspend --noflush device_name
After you resize your storage and take it back online, you must run the following command before resizing your paths: 
#  dmsetup resume device_name