Method and apparatus for differential backup in a computer storage system

Abstract

Method and apparatus for backup in restoring data on a computer system are disclosed. Backups may include a differential backup. In a differential backup, only some (but not all) segments of data in a primary copy are backed up. The segments may correspond to physical segments of storage in a storage system, rather than logical level segments of storage. The method and apparatus may include constructing a complete copy of a backed up element from an earlier full backup and a subsequent differential backup.

What is claimed is:  
     
         1 . A method of backing up data in a computer storage system, the data being stored in a plurality of identifiable segments, the method comprising steps of: 
 (a) at a first time, identifying which segments have been changed since a preceding backup; and    (b) forming a first backup that includes a copy of the identified changed segments and omits at least one of the segments that has not changed; and wherein 
 the identifiable segments are formed in units corresponding to physical segments of storage in the computer storage system.  
   
     
     
         2 . The method of  claim 1 , wherein the step (a) comprises a step of receiving a physical bit mask.  
     
     
         3 . The method of  claim 1 , wherein the computer storage system stores data according to a fixed block architecture and the identifiable segments correspond to blocks of data in the fixed block architecture.  
     
     
         4 . The method of  claim 1 , wherein: 
 the computer storage system stores data on at least one disk drive;    the disk drive includes at least one track; and    the identifiable segments correspond to tracks on the disk drive.    
     
     
         5 . The method of  claim 1 , further comprising steps of: 
 (c) at a second time, identifying which of the identifiable segments have been changed since the preceding backup; and    (d) forming a second backup that includes a copy of the changed identifiable segments, identified in step (c), and omits at least one of the segments that has not changed.    
     
     
         6 . The method of  claim 1 , further comprising steps of: 
 (c) at a second time, identifying which of the identifiable segments have been changed since the first time; and    (d) forming a second backup that includes a copy of the changed identifiable segments, identified in step (c), and omits at least one of the segments that has not changed.    
     
     
         7 . The method of  claim 1 , wherein 
 the identifiable segments constitute a logical element, each identifiable segment having a location in the logical element;    each identifiable segment is stored in a physical segment of memory; and    the step (a) comprises a step of 
 (e) mapping the locations of the identifiable segments in the logical element to the physical segments of memory.  
   
     
     
         8 . The method of  claim 7 , wherein the step (e) comprises a step of converting one or more physical bit masks into a logical bit mask.  
     
     
         9 . The method of  claim 1 , wherein: 
 the identifiable segments constitute a logical element, each identifiable segment having a respective location in the logical element; and    the step (b) comprises steps of forming a backup file including the identified changed segments and forming a differential bit map specifying the correspondence between the identified changed segments of the backup file and the location of the respective segment in the logical element.    
     
     
         10 . A backup storage system, comprising: 
 a differential backup generator to receive information specifying which physical segments of storage in a physical storage device have changed data and to generate a differential backup; and    a backup storage device to store the differential backup.    
     
     
         11 . The storage system of  claim 10 , wherein the backup storage device comprises a tape drive.  
     
     
         12 . The storage system of  claim 10 , further comprising the physical storage device, the physical storage device including means for tracking which of the physical segments have been changed since a preceding level zero backup.  
     
     
         13 . The storage system of  claim 10 , further comprising the physical storage device, the physical storage device including means for tracking which of the physical segments have been changed since a preceding differential backup.  
     
     
         14 . The storage system of  claim 10 , wherein the differential backup generator comprises means for mapping physical locations of the physical segments to logical locations of the physical segments within a logical element.  
     
     
         15 . The storage system of  claim 10 , wherein the differential backup generator comprises means for generating a differential bit file.  
     
     
         16 . The storage system of  claim 15 , wherein the differential backup generator further comprises means for generating a differential bit map for the differential bit file.  
     
     
         17 . A method of forming a complete backup copy of a plurality of segments of data in a computer storage system, the complete backup copy corresponding to the plurality of segments at a target time, the method comprising steps of: 
 (a) providing an earlier backup copy of the plurality of segments corresponding to an earlier time before the target time;    (b) providing a first later copy of at least one of the segments, corresponding to a time after the earlier time; and    (c) forming the complete backup from the earlier backup copy and the first later copy.    
     
     
         18 . The method of  claim 17 , 
 further comprising a step of providing a second later copy of at least one of the segments, corresponding to a time after the earlier time and before the time of the first later copy; and    wherein the step (c) comprises a step of 
 (d) forming the complete backup from the earlier backup copy, the first later copy and the second later copy.  
   
     
     
         19 . The method of  claim 18 , wherein the step (d) comprises a step of selectively copying segments from the earlier backup copy, the first later copy and the second later copy.  
     
     
         20 . A backup storage system, comprising: 
 means for storing an earlier backup copy of a plurality of physical segments constituting a logical element, the earlier backup copy corresponding to an earlier time, and for storing a first later copy of at least one of the segments, corresponding to a time after the earlier time; and    means for forming a complete backup from the earlier backup copy and the first later copy.    
     
     
         21 . The backup storage system of  claim 20 , wherein 
 the means for storing comprises means for storing a second later copy of at least one of the segments, corresponding to a time after the earlier time and before the time of the first later copy; and    the means for forming comprises means for forming the complete backup from the earlier backup copy, the first later copy and the second later copy.    
     
     
         22 . The backup storage system of  claim 20 , wherein 
 the means for storing comprises means for storing a second later copy of at least one of the segments, corresponding to a time after the earlier time and before the time of the first later copy; and    the means for forming comprises means for forming the complete backup from the earlier backup copy, the first later copy and the second later copy.    
     
     
         23 . A method of restoring information from a logical element stored in a computer system, the method comprising steps of: 
 forming a synthetic level zero copy of the logical element; and    restoring the information from the synthetic level zero copy.    
     
     
         24 . The method of  claim 23 , wherein the restored information is the full logical element.  
     
     
         25 . The method of  claim 23 , wherein the forming step comprises a step of forming the synthetic level zero copy from a backup copy of the logical element and a differential backup copy of a portion of the logical element.  
     
     
         26 . The method of  claim 23 , wherein the forming step comprises a step of forming the synthetic level zero copy from a backup copy of the logical element and a plurality of differential backup copies of respective portions of the logical element.  
     
     
         27 . A backup system for storing backups for a first time and a second time, the first time being earlier than the second time, of a logical element stored in a computer storage system, 
 a first memory unit storing a backup copy of a plurality of physical segments of memory, constituting the logical element, of the computer storage system, the backup copy corresponding to a first time; and    a second memory unit storing a later differential backup copy of at least one of the physical segments, corresponding to a time after the first time.    
     
     
         28 . The backup system of  claim 27 , wherein the second memory unit comprises a digital storage tape.  
     
     
         29 . The backup system of  claim 27 , further comprising a third memory storing a catalog to identify corresponding locations of the segments in the backup copy and the later copy.