Mapping Table Size

The second cost of log-structuring is the potential for extremely large mapping tables, with one entry for each 4-KB page of the device. With a large 1-TB SSD, for example, a single 4-byte entry per 4-KB page results in 1 GB of memory needed the device, just for these mappings! Thus, this page-level FTL scheme is impractical.

Block-based mapping

One approach to reduce the costs of mapping is to only keep a pointer per block of the device, instead of per page, reducing the amount of mapping information by a factor of $\frac {Size_{block}} {Size_{page}}$ ...