text: **Event ID**
  An event ID is a value that is used to identify a unique error condition that was detected by the 
  Storwize V7000. An event ID is used internally in the cluster to identify the error. 
  
  **Excluded condition**
  The excluded condition is a status condition. It describes an MDisk that the IBM Storwize 
  V7000 decided is no longer sufficiently reliable to be managed by the cluster. The user must 
  issue a command to include the MDisk in the cluster-managed storage. 
  
  **Extent**
  An extent is a fixed-size unit of data that is used to manage the mapping of data between 
  MDisks and volumes. The size of the extent can range 16 MB - 8 GB. 
  
  **External storage**
  External storage refers to MDisks that are SCSI logical units that are presented by storage 
  systems that are attached to and managed by the clustered system. 
  
  **Failback**
  Failback is the restoration of an appliance to its initial configuration after the detection and 
  repair of a failed network or component. 
  
  **Failover**
  Failover is an automatic operation that switches to a redundant or standby system or node in 
  a software, hardware, or network interruption. See also Failback. 