text: **Note:**An unmirrored volume can be migrated from one location to another by adding a 
  second volume copy at the required destination, waiting for the two copies to synchronize, 
  and then removing the original copy. This operation can be stopped at any time. The two 
  copies can be in different storage pools with different extent sizes. For more information, 
  see 7.7.2, “Volume migration by adding a volume copy” on page 285. 
  
  A volume with more than one copy can be checked to see whether all of the copies are 
  identical or consistent. If a medium error is encountered while it is reading from one copy, it is 
  repaired by using data from the other copy. This consistency check is performed 
  asynchronously with host I/O. 
  
  **Important:**Mirrored volumes can be taken offline if no quorum disk is available. This 
  behavior occurs because the synchronization status of mirrored volumes is recorded on 
  the quorum disk. 
  
  Mirrored volumes use bitmap space at a rate of 1 bit per 256 KiB grain, which means that 
  1 MiB of bitmap space supports up to 2 TiB of mirrored volumes. The default size of bitmap 
  space is 20 MiB, which enables up to 40 TiB of mirrored volumes. If all 512 MiB of variable 
  bitmap space is allocated to mirrored volumes, 1 PiB of mirrored volumes can be supported. 