Hw-requirement result, Hard disk performance figures, Hard disk write cache – Kofax Communication Server 9.1 User Manual

Page 78

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Environment Guide

Version 3.00.04

78

© Copyright Kofax, Inc. All information is subject to change without notice.

Adapt the 3 other input fields (“average message size in bytes”, “fax line usage per message in seconds”
and “average number of pages”) if the preset values do not fit. The “average message size in bytes” is the
size of the back-received documents, it only matters if the back-reception option is used.

The “peak

message throughput per hour

” value is calculated from the “fax line usage per message in seconds” input

value and the number of lines.

HW-Requirement Result

The result of the HW-

Requirement calculation appears in the “disk writes per second” and “average disk

access time in ms” fields. It is assumed here that there are no disk reads because a sufficiently large
TCOSS disk cache has been configured, so the disk access time in milliseconds can be calculated from the

disk writes alone.

Before selecting a hard

disk based on the disk writes per second add a “safety margin” of 50-100% to the

calculated figure, to allow for other use cases not taken into account by the HW-Requirement Calculator.

Also the KCS should not run on 100% disk usage in peak periods.

Hard Disk Performance Figures

Usually the hard disk access time can be looked up in the hard disk specification. The access time consists

of 2 parts: seek time and latency

average access time = average seek time + average latency

The average 2009 desktop hard disk has seek times of 9 or 10 milliseconds, while a fast server-grade hard

disk may show seek times of 2 to 4 milliseconds. The average latency (half a revolution) can be calculated

from the rotational speed of the disk:

RPM

5400

7200

10000

15000

Average latency

5.6 ms

4.2 ms

3 ms

2 ms

Here are some hard disk performance examples:

Hard disk

RPM

Latency

Avg seek time

Writes / sec

WD Caviar Blue 250 GB

7200

4.2 ms

8.9 ms

76

HP SAS enterprise 10000 rpm

10000

3 ms

4 ms

143

HP SAS enterprise 15000 rpm

15000

2 ms

3 ms

200

Hard Disk Write Cache

The hard disk write cache setting can be looked up under Drive

– Properties – Hardware – Properties –

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