Parity-Switched Data Placement: Optimizing Partial Stripe Writes in XOR-Coded Storage Systems

Erasure codes tolerate disk failures by pre-storing a low degree of data redundancy, and have been commonly adopted in current storage systems. However, the attached requirement on data consistency exaggerates partial stripe write operations and thus seriously downgrades system performance. Previous works to optimize partial stripe writes are relatively limited, and a general mechanism is still absent. In this paper, we propose a Parity-Switched Data Placement (PDP) to optimize partial stripe writes for any XOR-coded storage system. PDP first reduces the write operations by arranging continuous data elements to join a common parity element's generation. To achieve a deeper optimization, PDP further explores the generation orders of parity elements and makes any two continuous data elements associate with a common parity element. Intensive evaluations show that for tested erasure codes, PDP reduces up to 31.9 percent of write operations and further increases the write speed by up to 59.8 percent when compared with two state-of-the-art data placement methods.