When Address Remapping Techniques Meet Consistency Guarantee Mechanisms

Guaranteeing crash consistency is still one of the most expensive operations in traditional file systems because it causes redundant writes in a journaling file system, excessive read/writes in a log-structured file system, and tree-wandering problem in a copy-on-write file system. In this paper, we argue that such overhead can be significantly reduced by leveraging address remapping technique, which is already essential in many flash SSD devices. We thoroughly explore the potential of address remapping technique to ease the cost of guaranteeing consistency in two traditional file systems (i.e., Ext4 and F2FS) and one database system (i.e., MySQL). In particular, we introduce address remapping-based techniques to guarantee consistency, for file system journaling (i.e., SOJ and SDJ), segment cleaning (i.e., SSC), and application-level data journaling (i.e., SADJ). To evaluate the proposed techniques, we developed a PCIe SSD prototype, which exposes the address remapping capability to the upper layer as a share command. Our experimental results using the PCIe SSD with the share command confirms that the address remapping, though simple, is very effective in reducing the read/write amplification due to the conventional ways of guaranteeing consistency in the existing file systems and database applications.