Prompt and gradual migration schemes

Abstract

Provided are mechanisms for promptly or gradually migrating data from a read-only disk in a storage system to a replacement disk, where, during gradual migration, data is migrated when it is requested of the read-only disk.

What is claimed is: 
     
         1 . A method for migrating data in a storage system comprising a plurality of active extents and one or more replacement logical or physical drives, the method comprising:
 determining that an active extent of a storage system has entered read-only mode to become a read-only extent;   determining, based on a storage policy, whether the storage system should promptly migrate data or gradually migrate data;   based on determining that the storage system should promptly migrate data, copying data from the read-only extent to a replacement logical or physical drive as rapidly as possible; and   based on determining that the storage system should gradually migrate data, upon receiving a read request for a data unit in the extent, copying the data unit from the read-only drive to the replacement logical or physical drive, and upon receiving a write request for a data unit in the read-only extent, writing the data unit to the replacement logical or physical drive.