Raid Data Migration Through Stripe Swapping

A system and method for improving storage system operation is disclosed. A storage system includes a first tier with high-performance redundancy and a second tier with capacity efficient redundancy. The first tier and the second tier are built from the same storage devices in a storage pool so each storage device includes both the first and second tiers. The storage system stores write data initially to the first tier. When demand for the data falls below a threshold, the storage system migrates the write data to the second tier. This is done by changing the mapping of underlying physical locations on the storage devices where the write data is stored so that the underlying physical locations are logically associated with the second tier instead of the first tier. After remapping, the storage system also computes parity information for the migrated write data and stores it in the second tier.