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Title

A Prototype of Power Saving Storage Method RAPoSDA

AuthorSatoshi Hikida, Hiroki Oguri, Haruo Yokota

Journal/Book nameProc. of SRDS'14, , , pp. 339-340

Issue date2014, 10DOI

http://dx.doi.org/10.1109/SRDS.2014.64

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http://www.ieee.org/index.html

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Powered by T2R2 (Science Tokyo Research Repository)A Prototype of Power Saving Storage Method
RAPoSDA
Satoshi HIKIDA

Hiroki OGURI

Haruo YOKOTA

Department of Computer Science
Tokyo Institute of Technology
Japan
Email: hikida@de.cs.titech.ac.jp

Department of Computer Science
Tokyo Institute of Technology
Japan
Email: oguri.h.aa@m.titech.ac.jp

Department of Computer Science
Tokyo Institute of Technology
Japan
Email: yokota@cs.titech.ac.jp

Abstract—Because of the development of information technologies and the pervasiveness of cloud services, Reducing power
consumption in large scale storage systems becomes a very
important issue. Recently, we have proposed a method to solve
the problem called Replica Assisted Power Saving Disk Array(RAPoSDA) and verified its effectiveness. RAPoSDA utilizes a
primary backup configuration on both cache memories and disk
drives to ensure system reliability and it dynamically controls
the timing and targeting of disk access based on individual disk
rotation states. Until now, we have evaluated the effectivenessof RAPoSDA by using simulation program which we had developed. The evaluation shows that RAPoSDA achieves significantly
reducing power consumption. However, we have not evaluatedit effectiveness on the practical environment. In this paper, weintroduce the prototype system of RAPoSDA to evaluate thepower saving capability of RAPoSDA.
Keywords—large-scale storage, power reduction, reliabilityI.

Fig. 1.

Configuration of RAPoSDA

its configuration. We plan to evaluate the effectiveness ofRAPoSDA in practical environment and compare with MAID
using this prototype system.

I NTRODUCTION

Nowadays the storage systems owned enterprises and data
centers has become large-scale to preserve a number of digital
data. Therefore, reducing the power consumption of thesestorage systems are very important issue. There are several
researches tackle this problem, especially MAID[1] is one of
the most known the proposal to reduce the power consumptionof large scale storage systems. MAID separates its disk drives
to two types of disk group. One called cache disks and theanother called data disks. The data accessed frequently are
stored to few cache disks and then decreasing the accessfrequency to the many other data disks. Therefore these data
disks can sleep long enough time to reduce the total power
consumption of storage system. However, MAID does notconsider to maintain the reliability and the fixed number
cache disks may become the performance bottleneck. Whereas,
we have proposed a method to solve this problem called
Replica Assisted Power Saving Disk Array (RAPoSDA)[2] andverified its effectiveness. RAPoSDA utilizes a primary backup
configuration on both cache memories and disk drives to ensure
system reliability and it dynamically controls the timing andtargeting of disk access based on individual disk rotation states.
Until now, we have evaluated the effectiveness of RAPoSDAby using simulation program which we had developed. The
evaluation shows that RAPoSDA achieves significantly reducing power consumption. However, we have not evaluated it
effectiveness on the practical environment. In this paper, weintroduce the prototype system of RAPoSDA and describe

II.

OVERVIEW OF RAP O SDAFig. 1 shows the configuration of RAPoSDA. From thisfigure, RAPoSDA consists of several cache memories anddisk drives. In particular, disk drives are separated into twotypes of disks, one called cache disks and the other called
data disks. And then RAPoSDA use a write cache memory totemporarily maintain data. It is important to maintain reliability
when the data are in the volatile cache memory, so we provide
the cache memory with a primary backup configuration that
corresponds to the data disks and assume each cache memories
are connected to corresponding UPSs. In addition, RAPoSDA
can use some disks as cache disks like a MAID[1] to provide
larger read cache spaces.
We adopt the chained declustering [3] method for data
placement on data disks as a primary backup configurationthat tolerates disk failures. Chained declustering is a simple
but effective strategy for data placement that provides good
reliability and accessibility when the backup data is logicallylocated in the disk next to the primary. Cache memories arededicated to corresponding to the primary and backup of data.
We assume each cache memory connects to the corresponding
power supply which assured to avoid power accident by using
uninterruptible power supply(UPS) individually.
In RAPoSDA, the data were replicated to two copies(primary and backup) on both cache memories and data disks.
At first, a primary data is assigned to a corresponding data

disk and then written to the primary area of a cache memory
which is binding to a disk group(DG) which encloses the data
disk. The backup data of the primary data is written to thebackup area of the another cache memory which assigned randomly. Meanwhile, because of data disks employees chained
declustering[3] data placement policy, a backup data whichcorresponding to the i-th disk’s primary data is stored on((i + 1) mod NDD )-th disk, where NDD represents a numberof data disks.
A. Read/write behaviour of RAPoSDA
To handle write request, the data are initially written into
both the primary and backup layer of the cache memory. The
written data are gathered in a corresponding buffer location in
the cache memory of each individual disk that is responsiblefor storing the data. Buffered data are written onto theircorresponding data disks when the amount of buffered dataon the cache memory exceeds a predefined threshold.
read requests initially check the existence of data in thecache memory, followed by cache disks. The cache memory
has primary and backup layers, and both layers are searchedfor data. If the target data are in the cache memory or cachedisks, the data are returned without accessing the data disks.
If the data do not exist in the cache memory or cache disk,
the data are read from a data disk.
III.

E FFECTIVENESS OF RAP O SDA

Recently, we demonstrated the effectiveness of RAPoSDA
in our work [2]. In that work, we compared the performanceand power saving effects of RAPoSDA with modified MAID
in simulations with different ratios of read/write requests in theworkloads. The original version of MAID had no cache memory and no replication mechanism, so we added them to MAID
to make a fair comparison. The experimental results showedthat RAPoSDA and the modified MAID provide reduced
power consumption compared with a simple disk array with nopower saving mechanism. However, RAPoSDA was superior
to the modified MAID. From the performance perspective, thesimulation results showed that the average response time ofRAPoSDA was shorter than that of the modified MAID. Thus,
consideration of individual disk rotation is an effective method
for reducing the power consumption of storage systems, while
maintaining good performance.
IV.

P ROTOTYPE SYSTEM

In this section, we describe a prototype storage system forevaluation of our proposal called RAPoSDA. Figure 2 depicts
the configuration of our prototype system. The prototype system consists of a PC-based controller, host bus adapter(HBA),
and power measuring instrument.
The controller is built on Linux kernel 2.6.32-5-amd64
and implemented as a key value store written in Java. Inaddition, to avoid the file system’s cache mechanism we wrote
the C++ native codes to direct disk accesses using open(1)system call with O DIRECT flag and our prototype call thismodule via JNI mechanism. As host bus adapter, we employee
High Point Data Center 7280 which can attach up to 32
SATA HDD to one PC via PCI Express interface. The power
measuring instrument is HIOKI Memory Hilogger which hasFig. 2.

The configuration of prototype system

90 channel to measure the currents and volts. we use 4 channel
to measure one HDD power consumption. Two of them probe
12V line and grand line, the other probe 5V line and grandline, respectively.
Incidentally, we assume the buffers (or DRAM memorymodules) of RAPoSDA are connected to the power supply
independently each other. However, it is hard to organize sucha configuration on the actual commodity PC hardware. Wethink there are few affect whether each buffer connects tocorresponding power supply individually, the prototype has apower supply. Although the buffer share the power supply, wetreat the buffer as several number of buffers in logically.
V.

C ONCLUSION

In this paper, we describe the prototype system for evaluation of our proposal that called RAPoSDA in practical environment. the protype can configuration other type of storage
configuration, then we plan to compare with MAID. we haveevaluated and verified the effectiveness of RAPoSDA by using
simulation program base experiment. However, we do not its
actual effectiveness in practical environment.
In the future we plan more experimental evaluation using
real workloads to verify the effectiveness of RAPoSDA capability precisely. In addition we plan to compare the prototype
based experiment result with the result of simulation program
based evaluation.
ACKNOWLEDGMENT
This work is partly supported by Grants-in-Aid for Scientific Research from Japan Science and Technology Agency (A)(#22240005, #25240014).
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7239/2010, April 2012, pp. 138–149.
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