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*** Hale Landis *** [EMAIL PROTECTED] ***
*** Niwot, CO USA *** www.ata-atapi.com ***
>>May I make a suggestion? As in the ATA6 AV Feature Set
>>proposal a good definition of the command completion time
>>would be the time from the command register being
>>written to the last interrupt of the last sector transferred.
>That sounds like the definition that has been used for the last 50
>years to measure command execution time.
I then assume that everyone agrees that this is correct.
>>This allows true device performance to be measured, but requires
>>that the IDE driver, and associated structure includes a mechanism
>>to transfer the times beyond the kernel. This is highly OS specific, I
>>know, but it is the only true way to HDD performance without dedicated
>>hardware.
>Most hard disk performance measurement is by strange and poorly
>designed applications programs written by people that (in my
>experience and my opinion) really do not understand what they are
>doing and what they are trying to measure. An OS that had some device
>driver interface that returned the command execution time would
>certainly lead to even more of this software.
In general you are correct, but then there are exceptions. Some people
like to fully characterise HDD's by measuring head & cylinder skews,
transfer rates by zone, HDD command overhead, seek time versus seek
distance etc etc. In these cases such an interface provides the
accuracy required. That is all I would like to say.
>>At Philips we have modified the request structure to include a Start
>>Time and a Finish Time for a request. In such a way very accurate
>>HDD performance can be measured, such as head & track skews,
>>for example.
>But do you also return the time from the end of the previous command
>to the beginning of the command that was just executed? If you are
>not measuring that time then, I'm sorry, you are missing the SINGLE
>MOST IMPORTANT THING THAT AFFECTS HARD DISK DRIVE PERFORMANCE,
>ESPECIALLY CACHING PERFORMANCE.
Hale, you probably have a valid point that you would like to make here,
but I cannot extract it from this sentence. Would you please describe
what you are implying? If so, by direct email.
I can only assume that you are mean HDD command overhead or OS overhead.
All I can say is that we characterise HDD's not OS's and we do measure
HDD command overhead.
Regards,
Stephen.
--
Dr. Stephen Cumpson, Senior Scientist,
Group Storage Technologies, Building WY 1 45, (WY12),
Philips Research Labs., Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands
Tel.: +31 40 274 2762 Fax: +31 40 274 4927
Email: mailto:[EMAIL PROTECTED]
Web: http://www.research.philips.com/
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