linux-kernel - Re: defrag deployment status (was Re: [PATCH] ext4: allow defrag (EXT4_IOC_MOVE

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Message-ID: <87f94c371003080831n4d310e10i2b9badf4290f1ede@mail.gmail.com>
Date:	Mon, 8 Mar 2010 11:31:49 -0500
From:	Greg Freemyer <greg.freemyer@...il.com>
To:	jim owens <owens6336@...il.com>
Cc:	David Newall <davidn@...idnewall.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Jeff Garzik <jeff@...zik.org>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org, Akira Fujita <a-fujita@...jp.nec.com>
Subject: Re: defrag deployment status (was Re: [PATCH] ext4: allow defrag 
	(EXT4_IOC_MOVE_EXT) in 32bit compat mode)

On Mon, Mar 8, 2010 at 11:22 AM, jim owens <owens6336@...il.com> 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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