Re: defrag deployment status (was Re: [PATCH] ext4: allow defrag (EXT4_IOC_MOVE_EXT) in 32bit compat mode)

[Greg Freemyer]

On Mon, Mar 8, 2010 at 11:22 AM, jim owens <owens6336@xxxxxxxxx> wrote:
> David Newall wrote:
>> Christian Borntraeger wrote:
>>> Some bigger things are missing in the e4defrag tool:
>>> ...
>>> - overall layout considerations (e.g. putting files close to its
>>> directory or
>>>   use the atime to move often used files to the beginning of a disk etc.)
>>
>> Shouldn't oft-used files be placed closer to the middle?  If you place
>> them at the beginning of the file, it's only possible for the head-stack
>> to be close to the file from the inner direction.  Place them in the
>> middle and it's possible for the head-stack to be close from the outer
>> direction, too, which sounds like a doubling of probability.  It seems
>> that it's the least frequently used files that should be placed at one
>> end of the disk or the other.
>
> No.  Your logic would be correct if rotating disks had
> similar speed at all locations.  Current disks are much
> faster at the 0 end than at the middle or highest address.
>
> It is not unusual to see 2x difference in transfer speed
> so you always want the important stuff as low as possible.
>
> jim

Jim, I should know this, but is sector 0 on the outside edge, or the inner edge?

I assume outer so that the linear speed of the platter under the head
is faster and thus more data per second is passing under the head.

Greg
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