# THIS IS THE MASTER BRANCH.

# About
An energy-efficient device mapper target that can redirect block reads/writes to
different disks (SATA, SAS, SSD, PCM, SMR) and can potentially power/spin down
disks according to workload block IO characteristics. The aim is balanced
trade-off among power consumption, IO performance and storage capacity by
leveraging strengths of different disks.

# Key idea: 
Data grouping by caching most frequently accessed data blocks in the most
efficient disk (like SSD) to make the current device mapper green.  Workloads
that previously go across multiple disks can now be satisified mostly by the SSD
cache, and therefore the other disks can be spin down for power benefit.