Re: partitioning order and IO performance

[Ross Walker <rswwalker@xxxxxxxxx>]

On Dec 23, 2009, at 1:29 PM, John R Pierce <pierce@xxxxxxxxxxxx> wrote:

> Ross Walker wrote:
>> I think you might be confusing CAV with CLV of optical drives.
>> http://en.m.wikipedia.org/wiki/Constant_Angular_Velocity
>>
>
> no, I'm not.     most HD's ('green drives' complicate this some)  
> spin at
> a constant RPM, so the rotational latency is the same on the inner and
> outer tracks, an average of 1/2 turn, about 4mS for a 7200 rpm drive,
> and 2mS for a 15000rpm enterprise drive .   However, the data rate
> changes. so the outer tracks have more data on them, which is read  
> at a
> higher speed in megabytes/second

You know your right. I don't know what I was thinking, a rotation is a  
rotation and if it takes 4ms on the outer tracks then it takes 4ms on  
the inner tracks.

It is I who had to two mixed up. It would be CLV that would make the  
disk spin faster as it approached the inner tracks which is the only  
way rotational latency would decrease.

Sorry for the noise, we now continue with your regularly scheduled  
program.

-Ross

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