[CentOS] partitioning order and IO performance
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.
>>> 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...
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