[CentOS] partitioning order and IO performance

Timo Schoeler timo.schoeler at riscworks.net
Thu Dec 24 04:39:12 UTC 2009


On 12/23/2009 08:15 PM, Les Mikesell wrote:
> Timo Schoeler wrote:
>> 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.
> 
> But these days, nothing should ever be reading from swap, although you 
> might write a bit there.  If it does, buy some more RAM instead of 
> worrying about disk performance.

Sure, absolutely no question; *but* in the (ancient) times it was
important, it was 'nice' to have it as fast as possible, i.e. on the
fastest section(s) of the used HDs. So...

Timo


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