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5.4.3.4. Changing Mirrored Volume Configuration

You can increase or decrease the number of mirrors that a logical volume contains by using the lvconvert command. This allows you to convert a logical volume from a mirrored volume to a linear volume or from a linear volume to a mirrored volume. You can also use this command to reconfigure other mirror parameters of an existing logical volume, such as corelog.
When you convert a linear volume to a mirrored volume, you are creating mirror legs for an existing volume. This means that your volume group must contain the devices and space for the mirror legs and for the mirror log.
If you lose a leg of a mirror, LVM converts the volume to a linear volume so that you still have access to the volume, without the mirror redundancy. After you replace the leg, you can use the lvconvert command to restore the mirror. This procedure is provided in Section 7.3, “Recovering from LVM Mirror Failure”.
The following command converts the linear logical volume vg00/lvol1 to a mirrored logical volume. 
# lvconvert -m1 vg00/lvol1
The following command converts the mirrored logical volume vg00/lvol1 to a linear logical volume, removing the mirror leg. 
# lvconvert -m0 vg00/lvol1
The following example adds an additional mirror leg to the existing logical volume vg00/lvol1. This example shows the configuration of the volume before and after the lvconvert command changed the volume to a volume with two mirror legs. 
# lvs -a -o name,copy_percent,devices vg00
  LV                  Copy%  Devices
  lvol1               100.00 lvol1_mimage_0(0),lvol1_mimage_1(0)
  [lvol1_mimage_0]        /dev/sda1(0)
  [lvol1_mimage_1]        /dev/sdb1(0)
  [lvol1_mlog]            /dev/sdd1(0)
# lvconvert -m 2 vg00/lvol1
  vg00/lvol1: Converted: 13.0%
  vg00/lvol1: Converted: 100.0%
  Logical volume lvol1 converted.
# lvs -a -o name,copy_percent,devices vg00
  LV                  Copy%  Devices
  lvol1               100.00 lvol1_mimage_0(0),lvol1_mimage_1(0),lvol1_mimage_2(0)
  [lvol1_mimage_0]        /dev/sda1(0)
  [lvol1_mimage_1]        /dev/sdb1(0)
  [lvol1_mimage_2]        /dev/sdc1(0)
  [lvol1_mlog]            /dev/sdd1(0)