[CentOS] partitioning order and IO performance

Ross Walker rswwalker at gmail.com
Wed Dec 23 03:02:11 UTC 2009


On Dec 22, 2009, at 6:13 PM, Robert Nichols  
<rnicholsNOSPAM at comcast.net> wrote:

> Carlos Santana wrote:
>> Hi,
>>
>> Does mount point specification while partitioning (order in which I
>> specify /, /boot, swap etc..) affect performance? I am not sure about
>> the syntax, but I guess one can also specify address/block range  
>> while
>> partitioning. Does it affect IO performance? Probably a stupid
>> question, but just curious.. Any insights?
>
> Not a stupid question at all.  For ordinary disk drives the answer is
> yes, absolutely.  The outer tracks of a disk are physically longer,
> and any but the most ancient of disk drives will pack more sectors
> into those tracks.  Since the disk rotates at a constant RPM, more
> sectors per second pass under the head on the outer tracks.  The
> ratio of data rates for the outermost vs. innermost tracks is
> typically 2:1 or a bit higher.  Add to this the need for more and
> longer seeks for filesystems on the inner tracks (again, less data
> on each physical track), and the performance degrades even more.
>
> On most disks cylinder numbering starts at the outer tracks, but I
> have heard of disks that number their cylinders in the opposite
> direction -- never actually seen one, though.

Also, for random IO the opposite is true, the rotational latency is  
significantly smaller on the inner tracks than the outer tracks, so  
random OPs perform better there.

Though having different workloads on opposite sides of the disk is  
counter productive, but say you had one large volume for random IO  
workloads and another large volume for sequential workloads, you could  
allocate the beginning chunk to your most performance oriented servers  
on the sequential volume and the end chunk to your most performance  
oriented servers on the random volume.

-Ross



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