Kofax Communication Server 9.1 - Manual (Page 78)

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 –
Policies: