“Command completion time measurement tool White Paper
IDEMA JAPAN Consumer HDD committee
ChairmanVice Chairman
Vice Chairman
Ryosuke Shimizu
Seiji Kawagoe
Shoji Tanaka
Matsushita Electric
Toshiba Co. Digital
SONY Co. Chemical Device
Industrial Co., Ltd.
Media Network Company
Business Group
1-15 Matsusuo-cho,
Disc & Memory Device Div
Kadomacity
1-1 Shibaura 1, Minato-ku
5-1-12 kitashinagawa
Osaka, JAPAN 571-8504
Tokyo, JAPAN 105-8001
shinagawa-ku Tokyo
Phone: 81-50-3487-3377
81-3-3457-2463
81-3-5448-2549
Fax:
81-6-6905-4608
81-3-5444-9400
81-3-5448-3257
shimizu.ryosuke@jp.panasonic.com seiji.kawagoe@toshiba.co.jp shoji.tanaka@jp.sony.com

1. Introduction
The purpose of this white paper is to introduce testing method which is good for designing
PVR application design. These two methods give the parameter about which CE makerdiscuss about CE application of HDD with an HDD maker.
Two procedures are explained in this white paper. The first is a simple testing procedurethat involves only a sequential access to HDD and a simple data analysis method. The other isa detailed testing procedure that involves HDD access with seek and a detailed but rather
complex data analysis method. In AV application, the meaning of HDD performance differsfrom that in IT application. The best case in access speed is not as important as sustaining
responses below a certain level. Both procedures share the same goal to detect the rate andmagnitude of responses and offer a way to analyze AV performance numerically.

2. Simple benchmark
1. 1ch Read in all surfaces
2. Sequential
3. every 128KB (256 sectors)
4. make Command Completion time to histogram2) Purpose

1. Firm wear mature ness
2. Head and Media reliability
3. HDD relative evaluation : initial - Life test3) Example

Case1

Case2

系列1

Response Count

1000000

1000000
10000010000
1000
100101100000
10000
系列1

1000
10010-9010027
0-70-50-10(ms)-301-10-20-30-40-50-60-70-80-90
10 1000270ERR

Response Count1) Method(ms)2008/06/09

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3. Detailed benchmark
A. Procedurea) Seek pattern
Three seek patterns, Outer-to-Inner, Inner-to-Outer, and Middle-to- Zigzag, are usedin this test method. The default head position is fixed for each pattern, the outermost track for
Outer-to-Inner, the innermost track for Inner-to-Outer, the track where max_LBA/2 is locatedfor Middle-to-Zigzag. The commands to be measured are issued when the head is tracking
the default position. After the command completion, the head is again positioned on thedefault track. Figure 1, 2, and 3 show each test pattern.
b) Measured Commands
It is recommended to perform the test under a fast host data transfer mode such as
Ultra DMA Mode 4. Under a slow host transfer mode, the host data transfer dominates thecommand completion time, and it becomes difficult to observe HDD characteristics such as
seek speed. The sector count per command is fixed at 256 sectors. Time duration between acommand register write and a command completion interrupt is measured as commandcompletion time. The seek distance in terms of LBA and the command completion time arerecorded.
c) Seeking the default track and SEEK command problem
After each command completion time measurement, the head must be positioned on
the default track. In order to do so, SEEK command might come up as the reasonable way.
However, there are some problems in how SEEK command is implemented in HDD’s. Somedrives return SEEK command completion even though the head is not tracking on the target
track. If a command completion time is measured under such a condition, an accurate
measurement becomes impossible since the default head position is not fixed.
In order to avoid this problem, the following method is used. When READ commandis measured, WRITE command is used to position the head on the default track and viceversa. The reason to use the opposite command to seek the default position is that the samecommand as measured command is unable to ensure actual seek if the cache is enabled.

Read Test
Cache
Write Test
Cache

MeasuredCommandREADOn
OffWRITE
OnOffSeek
WRITE
OffREAD
OffTab. 1: Measured Command and Seek Command

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Fig. 1: Outer-to-Inner Test PatternFig. 2: Inner-to-Outer Test Pattern

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3 of 6IDEMA-JAPAN “Command completion time measurement tool“ProposalFig. 3: Mid-to-Zigzag Test Pattern

B. Data Analysis
Figure 4 shows an example of test results. The target HDD is a typical 5400rpm
80GB HDD.

Fig. 4: Example of Read Test Result

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In the figure, a belt of data points with a width of approximately 11msec is observed.
Data points that belong to this data belt are considered as command completions withoutretries. The belt width corresponds to the drive’s rotational latency. In this drive’s case, therevolution period is about 11msec and matches with the width of the belt. The lower boundaryof the belt indicates the command completions without retries and rotational latencies. The
belt’s lower boundary draws an increasing curve, and it indicates increasing seek time.
A distribution and magnitude of retires are a major interest in AV-HDD performanceanalysis. The depth of retry corresponds to the number of disk revolutions taken for thecommand completion. Generating a histogram with respect to command completion time canprovide some information of retry distribution. However, a seek curve makes separation ofcommand completions with respect to the disk revolution impossible. In order to solve thisproblem, the data modification is proposed.
By subtracting the belt’s lower boundary curve, the overall data can be made flat andthe data points can be separated into each disk rotational period. The lower boundary iscalculated as the following. First, local minimum points for every 6000 samples are extracted
from the original data. Then, the curve is obtained by applying a linear interpolation to theextracted local minimum points. An example is shown in Figure 5.

Fig. 5: Lower Boundary Curve

By subtracting the lower boundary curve, the data can be made flat as shown inFigure 6.

Fig. 6: Flat Data

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A histogram with respect to the command completion time without overhead isobtained. The result is shown in Figure 7. In the figure, areas separated by dashed lines
represent the disk rotational period. The revolution number corresponds to the depth of retries.
As a result, the frequency of retries with respect to the retry depth can be numericallyobtained.

Fig. 7: Histogram

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