iDiscard: Enhanced Discard() Scheme for Flash Storage Devices

摘要

NAND flash storage devices have become one of the fundamental building blocks in cloud computing systems because they provide fast responsiveness and low-power consumption compared with HDDs. Unfortunately, flash storage devices still suffer from the semantic gap between the file system and the flash storage device. In this paper, we first answer a simple question: Is Discard() command still a research issue? We then propose an enhanced Discard() scheme, called iDiscard, to completely bridge the semantic gap between the current ext4 file system and flash storage devices. The key idea is that iDiscard dynamically invalidates flash pages mapped to the obviated inode blocks of the file system. For evaluation, we implemented iDiscard on the current ext4 file system and then compared it on the Disksim simulator and a real SSD, Samsung 850 PRO SSD. Our experimental results clearly show that iDiscard efficiently reduces the number of pages in the flash storage, that are valid but contain metadata for removed files, by up to 5.4x compared with existing ext4 file system.