Optimizing Power Consumption

I recently reviewed an interesting paper, titled - Optimizing Power Consumption in Large Scale Storage Systems. Even though I was impressed by the lucid presentation of the problem and the quality of the proposed solution, the true significance of the work dawned upon me only after I watched Al Gore's movie - The Inconvenient Truth. Yes, three years after the movie won the Academy award for best documentary, I finally borrowed it from the library and watched it at home with my family.

Anyhow, the many objective of this post is to highlight some interesting aspects of the paper on optimizing power consumption. The paper highlights the reality of present time, where huge data centers have become a way of life. These data centers contain thousands of servers for storage, which in turn results in higher electric bills and searing heat. Hard disks account for a significant portion of the energy consumption and in a data center many hard disks are not accessed at a given time. The paper explains the three existing disk management solutions - Hardware-based solutions, Disk Management solutions and Caching solutions - that attempt to conserve power by powering down hard drives that are not being used. The paper outlines the limitations of these existing solutions, as not being able to predict well on which disks to power down, and then presents a fourth option - File-system solution, where the Log-structured File System (LFS) directs all writes to the log head. This leads to a perfect prediction mechanism as the disk being written to is known in advance and other disks may be powered down or operated in low-power mode.

LFS was initially motivated by the desire to optimize latency of write-accesses. To eliminate seek time, LFS replaces write operations by append, and the secondary storage is treated as a large append-only log, where writes go to the log head. Reads don't avoid the seek latency, however, the assumption is that with a good caching technique, there would be limited reads that need to access the secondary storage.

The paper finds a new fit for an old idea - using LFS to optimize the power consumption in a data center. Even though the idea sounds impressive at a conceptual level, there is still more work - related to the efficacy of log cleaning approach - that needs to be done before this idea turns into a viable solution. Overall this was an interesting read, with the significance of the work being exemplified by the wonderful movie - An Inconvenient Truth.