Leveraging SSD's Flexible Address Mapping to Accelerate Data Copy Operations.

On-disk data copy is commonly performed in various software. Its current implementation with read and write commands needs to go through the I/O stack, introducing significant performance overhead. Actually when only one disk is involved in a copy operation, the data do not have to be read out of the device and the operation can be all performed within it. Furthermore, if the device is an SSD supporting flexible mapping from logical to physical addresses, the data do not need to be physically duplicated and the data copy purpose can be fulfilled by establishing a new address mapping. In the paper, we propose a copy primitive for SSD to support copy of block(s) of data within a device with an almost zero cost regardless of amount of data. We show that it is relatively easy to implement the primitive, named copyless copy, or CC in short. We also evaluate two example uses of CC, database journaling and block-level deduplication, where the new primitive can help for efficient data copy as the case study. Our experiments with the use cases show that CC can dramatically increase the software's performance, reduce data writes to the device for improving SSD's endurance and space efficiency.