Methods and system for reserving storage space for data migration in a redundant hierarchic data storage system by dynamically computing maximum storage space for mirror redundancy

摘要

A hierarchic disk array data storage system has multiple storage disks that define a physical storage space and a RAID management system that maps the physical storage space into two virtual storage spaces. The RAID-level virtual storage space presents the physical storage space as mirror and parity RAID areas where the mirror RAID areas contain mirror allocation blocks to store data according to RAID Level 1 and the parity RAID areas contain parity allocation blocks to store data according to RAID Level 5. The application-level virtual storage space presents the physical storage space as multiple virtual blocks. The RAID management system migrates data between the mirror and parity RAID areas to optimize performance and reliability. To ensure that sufficient space is retained for this migration, the RAID management system limits the number of virtual blocks that are allocated in the mirror RAID areas. The maximum number of virtual blocks in mirror RAID areas is dynamically computed based upon a function of the physical capacity of the storage disks, the number of storage disks, and the allocated capacity at the time of each storage request from the user.