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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
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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
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  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
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  4. Resize your multipath device by running the multipathd resize command: 
    # multipathd -k'resize map mpath0'
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  5. Resize the filesystem (assuming no LVM or DOS partitions are used): 
    # resize2fs /dev/mapper/mpath0
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For further information on resizing an online LUN, see the Online Storage Reconfiguration Guide.
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