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

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Date:	Mon, 08 Mar 2010 14:38:50 -0500
From:	Valdis.Kletnieks@...edu
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, 08 Mar 2010 11:22:15 EST, jim owens said:

> 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.

On the flip side, seek time is so much larger than the time spent
actually reading that minimizing the seeks will improve total throughput
more.  Sure, maybe you spend 0.05ms reading instead of 0.1ms - but if
the seek took 0.75ms rather than 0.5ms you're still in the hole.

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