[CentOS] partitioning order and IO performance

Les Mikesell lesmikesell at gmail.com
Wed Dec 23 19:15:56 UTC 2009


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.

-- 
   Les Mikesell
    lesmikesell at gmail.com



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