Creation and Management of Logical Volume Snapshots Under Hierarchical Storage System

Abstract

The method of the present invention includes the steps of: receiving a command for creating a snapshot of the logical volume; preparing a management table for managing the snapshot; detecting the storage status of the logical volume; and updating the management table without recalling the logical volume from the second level storage to the first level storage when the logical volume has migrated from the first level storage to the second level storage. After the update, the storage table indicates whether creation of a snapshot is required, whether a logical volume has migrated, and whether the second level storage is the storage location of the logical volume.

1 . A method for creating and managing snapshots of hierarchically managed logical volumes in a storage system including first level storage and second level storage lower than the first level storage, the method comprising:
 receiving a command for creating a snapshot of the logical volume;   preparing, using a processor and a memory, a management table for managing the snapshot, the management table including first metadata indicating the creation status of the snapshot, second metadata indicating the management status of the snapshot, and third metadata indicating the storage location of the logical volume;   detecting the storage status of the logical volume; and   updating the management table without recalling the logical volume from the second level storage to the first level storage when the logical volume has migrated from the first level storage to the second level storage, the first metadata indicating that creation of a snapshot is required, the second metadata indicating that the logical volume has migrated, and the third metadata indicating that the second level storage is the storage location of the logical volume.   
     
     
         2 . The method according to  claim 1  further comprising:
 recalling the logical volume when access to the logical volume or the snapshot is requested; 
 creating a snapshot from the logical volume recalled to the first level storage; and 
 updating the management table, the first metadata indicating that the snapshot has been created, the second metadata indicating that the logical volume has pre-migrated, and the third metadata indicating that the second level storage is the storage location of the logical volume. 
 
     
     
         3 . The method according to  claim 1  further comprising:
 updating the management table when overwriting of the logical volume or deletion of the logical volume is requested, the first metadata indicating that creation of a snapshot is not required, the second metadata indicating that the logical volume has migrated, and the third metadata indicating that the second level storage is the storage location of the logical volume. 
 
     
     
         4 . The method according to  claim 1  further comprising:
 updating the management table when overwriting of the snapshot is requested, the first metadata indicating that creation of a snapshot is not required, the second metadata indicating that the logical volume is located in the first level storage, and the third metadata indicating that deletion has been performed. 
 
     
     
         5 . The method according to  claim 1  further comprising:
 updating the management table when deletion of the snapshot is requested, the first metadata indicating that deletion has been performed, the second metadata indicating that deletion has been performed, and the third metadata indicating that deletion has been performed. 
 
     
     
         6 . The method according to  claim 1  further comprising:
 creating a snapshot of the logical volume in the first level storage when the logical volume is stored in the first level storage or stored in both the first level storage and the second level storage; and 
 updating the management table, the first metadata indicating that the snapshot has been created, the second metadata indicating that the logical volume is stored in the first level storage or is stored in both the first level storage and the second level storage, and the third metadata indicating that the second level storage is not the storage location of the logical volume or the second level storage is the storage location of the logical volume. 
 
     
     
         7 . The method according to  claim 1 , wherein the first level storage includes a hard disk drive (HDD), and the second level storage includes a tape drive.