[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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