  The emerging interlaced magnetic recording (IMR) technology achieves a higher
areal density for hard disk drive (HDD) over the conventional magnetic
recording (CMR) technology. IMR-based HDD interlaces top tracks and bottom
tracks, where each bottom track is overlapped with two neighboring top tracks.
Thus, top tracks can be updated without restraint, whereas bottom tracks can be
updated by the time-consuming read-modify-write (RMW) or other novel update
strategy. Therefore, the layout of the tracks between the IMR-based HDD and the
CMR-based HDD is much different. Unfortunately, there has been no related disk
simulator and product available to the public, which motivates us to develop an
open-source IMR disk simulator to provide a platform for further research. We
implement the first public IMR disk simulator, called IMRSim, as a block device
driver in the Linux kernel, simulating the interlaced tracks and implementing
many state-of-the-art data placement strategies. IMRSim is built on the actual
CMR-based HDD to precisely simulate the I/O performance of IMR drives. While
I/O operations in CMR-based HDD are easy to visualize, update strategy and
multi-stage allocation strategy in IMR are inherently dynamic. Therefore, we
further graphically demonstrate how IMRSim processes I/O requests in the
visualization mode. We release IMRSim as an open-source IMR disk simulation
tool and hope to attract more scholars into related research on IMR technology.
