FAST '08 – Abstract
Pp. 253–267 of the Proceedings
Write Off-Loading: Practical Power Management for Enterprise Storage
Dushyanth Narayanan, Austin Donnelly, and Antony Rowstron, Microsoft Research Ltd.
In enterprise data centers power usage is a problem impacting server
density and the total cost of ownership. Storage uses a significant
fraction of the power budget and there are no widely deployed
power-saving solutions for enterprise storage systems. The traditional
view is that enterprise workloads make spinning disks down ineffective
because idle periods are too short. We analyzed block-level traces
from 36 volumes in an enterprise data center for one week and concluded
that significant idle periods exist, and that they can be further
increased by modifying the read/write patterns using write
off-loading. Write off-loading allows write requests on spun-down
disks to be temporarily redirected to persistent storage elsewhere in
the data center.
The key challenge is doing this transparently and efficiently at the
block level, without sacrificing consistency or failure resilience.
We describe our write off-loading design and implementation that
achieves these goals. We evaluate it by replaying portions of our
traces on a rack-based testbed. Results show that just spinning disks
down when idle saves 28–36% of energy, and write off-loading further
increases the savings to 45–60%.
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