Patent ID: 6467024
Filing Date: 2002-10-15
Classification: G06F

Abstract:
A method for accessing identifiable data volumes from a plurality of data storage libraries in response to recall requests, said data storage libraries storing redundant copies of said identifiable data volumes, said data storage libraries having cache storage and backing storage, said identifiable data volumes each directly associated with an updatable synchronization token, said synchronization token indicating the relative update levels of said directly associated redundant copies, said data storage libraries coupled to a plurality of directors, each said data storage library migrating data volumes from said cache storage to said backing storage, said recall requests forwarded from said directors additionally requesting said directly associated synchronization tokens, said method comprising the steps of:said data storage library maintaining said synchronization token directly associated with said data volume; said data storage library identifying each of said data volumes upon being stored in said cache storage of said data storage library; said data storage library identifying each of said data volumes migrated to and stored in said backing storage of said data storage library; and said data storage library responding to said recall request for one of said redundant copies of said identifiable data volumes, providing, with said synchronization token directly associated with said identifiable data volume, an indicator, responsive to said identifying steps, which indicates whether said identifiable data volume is identified as currently stored in said cache'storage or said backing storage, whereby the performance of said accessing is increased by a selection of a redundant copy of said identifiable data volume identified as stored in said cache storage rather than a copy identified as stored in said backing storage.