Storage Controller Extent Pool Management for Thrashing Reduction

The patent applies preliminary action by pre-allocating secondary allocation space and maintaining a pool of pre-available extents. When primary allocation space is exhausted, the system can immediately allocate from the secondary space without triggering frequent extent allocation/deallocation cycles. This advance preparation eliminates the thrashing that occurs with dynamic extent management, thereby maintaining storage subsystem performance while still achieving efficient space utilization through the thin provisioning model.

The patent applies local quality by creating different states for different portions of allocated space. The secondary allocation space is marked with a specific indicator (bit) that distinguishes it from normally allocated space. This local differentiation allows the system to track which extents are available for the extent pool without fully releasing them, providing both space availability and system stability by maintaining a known, deterministic state for these extents rather than leaving them in an indeterminate condition.

The patent applies merging by integrating the secondary allocation space management into the existing thin provisioning infrastructure. The secondary allocation space is managed as an extension of the primary allocation space, using the same extent pool and allocation mechanisms. The indicator bit is incorporated into the existing extent metadata structures. This unified approach allows the system to reduce thrashing and improve performance while minimizing the increase in device complexity by leveraging existing components rather than introducing entirely new management systems.