FSIMR: File-system-aware Data Management for Interlaced Magnetic Recording

Interlaced Magnetic Recording (IMR) is an emerging recording technology for hard-disk drives (HDDs) that provides larger storage capacity at a lower cost. By partially overlapping (interlacing) each bottom track with two adjacent top tracks, IMR-based HDDs successfully increase the data density while incurring some hardware write constraints. To update each bottom track, the data on two adjacent top tracks must be read and rewritten to avoid losing their valid data, resulting in additional overhead for performing read-modify-write (RMW) operations. Therefore, researchers have proposed various data management schemes to mitigate such overhead in recent years, aiming at improving the write performance. However, these designs have not taken into account the data characteristics of the file system, which is a crucial layer of operating systems for storing/retrieving data into/from HDDs. Consequently, the write performance improvement is limited due to the unawareness of spatial locality and hotness of data. This paper proposes a file-system-aware data management scheme called FSIMR to improve system write performance. Noticing that data of the same directory may have higher spatial locality and are mostly updated at the same time, FSIMR logically partitions the IMR-based HDD into fixed-sized zones; data belonging to the same directory will be arranged to one zone to reduce the time of seeking to-be-updated data (seek time). Furthermore, cold data within a zone are arranged to bottom tracks and updated in an out-of-place manner to eliminate RMW operations. Our experimental results show that the proposed FSIMR could reduce the seek time by up to 14% without introducing additional RMW operations, compared to existing designs.