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Chapter 5. DM-Multipath Administration and Troubleshooting

This chapter will provide information on administering DM-Multipath on a running system. It includes sections on the following topics:
  • Resizing an Online Multipath Device
  • The Multipath Daemon
  • Issues with Large Number of LUNs
  • Issues with queue_if_no_path feature
  • Multipath Command Output
  • Multipath Queries with multipath Command
  • Multipath Command Options
  • Multipath Queries with dmsetup Command
  • Troubleshooting with the multipathd Interactive Console

5.1. Resizing an Online Multipath Device

If you need to resize an online multipath device, use the following procedure.
  1. Resize your physical device.
  2. Use the following command to find the paths to the LUN: 
    # multipath -l
  3. Resize your paths. For SCSI devices, writing a 1 to the rescan file for the device causes the SCSI driver to rescan, as in the following command: 
    # echo 1 > /sys/block/device_name/device/rescan
  4. Resize your multipath device by running the multipathd resize command: 
    # multipathd -k'resize map mpath0'
  5. Resize the filesystem (assuming no LVM or DOS partitions are used): 
    # resize2fs /dev/mapper/mpath0
For further information on resizing an online LUN, see the Online Storage Reconfiguration Guide.