Efficient snapshot method for all-flash array

An all-flash array (AFA) equipped with solid state drives (SSDs) is the high-reliability, high-performance and large-capacity data storing system. Snapshot is used as a data backup function and one of existing methods of snapshot is Copy on Write (CoW). However, CoW consumes the memory bandwidth of storage controller (SC) because of chunk copies and isn't suitable for a AFA. Therefore, we propose an efficient snapshot method named Mapping Switching in Flash Translation Layer (MSiF). Instead of physical data transfers by a SC, MSiF rewrites the SSD's logical-physical address translation table using Flash Translation Layer in SSDs. A difference occurs between current data and backup data due to an updating data, and a SC can overwrite the current data by switching a mapping of the logical-physical translation table in a SSD without physical data transfer. Therefore, the amount of data transfer to SSDs and paths in SCs decreases. We estimate the performance right after taking snapshots using an evaluation model; compared to CoW, MSiF reduce the time, which it takes to recover the temporary throughput degradation due to taking a snapshot, by up to 76.9 %, and reduce the response time by up to 56.5 %, in the case of chunk size 128 kBytes.