text: **Hot extent**
  A hot extent is a frequently accessed volume extent that gets a performance benefit if it is 
  moved from an HDD onto a Flash Disk. 
  
  **Hot Spare node (SVC only)**
  Hot Spare Node is an online SVC node defined in a cluster, but not in any IO group. During a 
  failure of any of online nodes in any IO group of cluster, it is automatically swapped with this 
  spare node. After the recovery of an original node has finished, the spare node returns to the 
  standby spare status. This feature is not available for IBM Storwize V7000. 
  
  **HyperSwap**
  Pertaining to a function that provides continuous, transparent availability against storage 
  errors and site failures, and is based on synchronous replication. 
  
  **Image mode**
  Image mode is an access mode that establishes a one-to-one mapping of extents in the 
  storage pool (existing LUN or (image mode) MDisk) with the extents in the volume. See also 
  “Managed mode” on page 780 and “Unmanaged mode” on page 787. 
  
  **Image volume**
  An image volume is a volume in which a direct block-for-block translation exists from the 
  MDisk to the volume. 
  
  **I/O Group**
  Each pair of IBM Storwize V7000 canisters is known as an input/output (I/O) Group. An I/O 
  Group has a set of volumes that are associated with it that are presented to host systems. 
  Each V7000 canister is associated with exactly one I/O Group. The canister in an I/O Group 
  provide a failover and failback function for each other. 