5.4.16.2. Converting a Linear Device to a RAID Device

You can convert an existing linear logical volume to a RAID device by using the --type argument of the lvconvert command.
The following command converts the linear logical volume my_lv in volume group my_vg to a 2-way RAID1 array. 
# lvconvert --type raid1 -m 1 my_vg/my_lv
Since RAID logical volumes are composed of metadata and data subvolume pairs, when you convert a linear device to a RAID1 array, a new metadata subvolume is created and associated with the original logical volume on (one of) the same physical volumes that the linear volume is on. The additional images are added in metadata/data subvolume pairs. For example, if the original device is as follows: 
# lvs -a -o name,copy_percent,devices my_vg
  LV     Copy%  Devices     
  my_lv         /dev/sde1(0)
After conversion to a 2-way RAID1 array the device contains the following data and metadata subvolume pairs: 
# lvconvert --type raid1 -m 1 my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
  LV               Copy%  Devices                      
  my_lv            6.25   my_lv_rimage_0(0),my_lv_rimage_1(0)
  [my_lv_rimage_0]        /dev/sde1(0)                 
  [my_lv_rimage_1]        /dev/sdf1(1)                 
  [my_lv_rmeta_0]         /dev/sde1(256)               
  [my_lv_rmeta_1]         /dev/sdf1(0)
If the metadata image that pairs with the original logical volume cannot be placed on the same physical volume, the lvconvert will fail.