[CentOS] partitioning order and IO performance

Timo Schoeler timo.schoeler at riscworks.net
Wed Dec 23 18:36:42 UTC 2009


On 12/23/2009 07:29 PM, John R Pierce 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

That's why in ancient times one was setting up partitions so that the
swap area was the the beginning (mostly the outer tracks of the HD --
never hit a drive that did it the other way round) of the drive.

Try it yourself, get a spare HD and create three partitions on it, two
smaller ones at beginning/end of the drive, the third one filling the
gap between them; install bonnie++ and compare the transfer rates.

Timo


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