NAND flash memory-based hybrid file system for high I/O performance

As the performance potentials of SSD (Solid State Device) have been recognized, adopting SSD to IT products as HDD replacements is rapidly increasing. Since SSD is organized into multiple flash memory packages, it deploys peculiar device characteristics that do not occur in HDD, such as block-unit erasure overhead. Also, its high cost per capacity is the main obstacle to building a large-scale storage subsystem with only SSDs. An alternative is to build a hybrid storage subsystem where a small portion of SSDs are integrated with HDDs so as to utilize SSD’s performance advantages in a cost-effective way. This study introduces a new form of file system, called N-hybrid (New-Form of hybrid file system), that enables us to support the hybrid device structure combined with both HDD and SSD. Our primary objectives in developing N-hybrid are to provide better I/O bandwidth by exploiting the characteristics of HDD and SSD and to provide a flexible data layout maximizing the usage of tight SSD storage resources. Several experiments were conducted to verify the effectiveness and suitability of N-hybrid.

► N-hybrid provides a flexible data layout to maximize SSD storage space.
► N-hybrid provides better I/O bandwidth by exploiting SSD and HDD devices.
► Mapping to the appropriate data section is possible for better I/O bandwidth.
► N-hybrid tries to alleviate FTL overhead by using data alignment.