text: **Effective capacity**
  See “Capacity” on page 771. 
  
  **Encryption key**
  The encryption key, also known as master access key, is created and stored on USB flash 
  drives or on a key server when encryption is enabled. The master access key is used to 
  decrypt the data encryption key. 
  
  **Encryption key server**
  An internal or external system that receives and then serves existing encryption keys or 
  certificates to a storage system. 
  
  **Encryption of data-at-rest**
  Encryption of data at rest is the inactive encryption data that is stored physically on the 
  storage system. 
  
  **Evaluation mode**
  The evaluation mode is an Easy Tier operating mode in which the host activity on all the 
  volume extents in a pool are “measured” only. No automatic extent migration is performed. 
  
  **Event (error)**
  An event is an occurrence of significance to a task or system. Events can include the 
  completion or failure of an operation, user action, or a change in the state of a process. 
  
  **Event code**
  An event code is a value that is used to identify an event condition to a user. This value might 
  map to one or more event IDs or to values that are presented on the service window. This 
  value is used to report error conditions to IBM and to provide an entry point into the service 
  guide. 