text: Figure 12-76 MDisk encryption state 
  
  When working with MDisks encryption, take extra care when configuring MDisks and pools. 
  
  If the MDisk was earlier used for storage of unencrypted data, the extents can contain stale 
  unencrypted data. This issue occurs because file deletion only marks disk space as free. The 
  data is*not*removed from the storage. Therefore, if the MDisk is not self-encrypting and was a 
  part of an unencrypted pool, and later was moved to an encrypted pool, it contains stale data 
  from its previous life. 
  
  Another mistake that can occur is to misconfigure an external MDisk as self-encrypting, while 
  in reality it is not self-encrypting. In that case, the data written to this MDisk is not encrypted 
  by Storwize V7000 because Storwize V7000 is convinced that the MDisk encrypts the data. 
  At the same time, the MDisk does not encrypt the data because it is not self-encrypting, so 
  you end up with unencrypted data on an extent in an encrypted pool. 
  
  However, all data that is written to any MDisk that is a part of correctly configured encrypted 
  pool is going to be encrypted. 