LVM and partition location

[Tony Arnold]

On Mon, 2006-08-14 at 00:41 +0100, Gabriel Dragffy wrote:
> David Abrahams wrote:
> 
> >It's often recommended to keep your swap/, var/ and tmp/ near the
> >center of a drive for speed reasons, but as far as I know LVM gives
> >you little control over the physical location of logical volumes.  How
> >do LVM users normally handle this?
> >
> >Thanks in advance,
> >
> >  
> >
> 
> Am I mistaken in thinking that it's actually the outter edges of the 
> platter that reap the highest performance. Imagine if you run in a 1 
> metre circle in 1 second, and then "push out" a little further to, say, 
> 3 metres, but you must still travel this distance in one second so 
> you're going to go faster. The outside of a hard disc platter must 
> travel more quickly to stay with the inside of the platter, thus 
> increasing the the head travel. Also more data can be stored 
> consecutively in the larger outside margins of a platter. I ain't got 
> nothing to back this up, and can't give anything scientific, so I can 
> well understand if I am misplaced in my assumptions.

The reason the middle of the disk is 'fastest' is due to the seek time
of the heads not the spin rate of the disk. On average, the middle
cylinders have the least distance for the heads to travel to reach them.

I believe you are right above though. Modern disks tend to have more
blocks per track on the outer tracks than they do on the inner tracks.
This helps to keep the density of data on the disk as high as it can be
over the whole area of the disk.

Having said that, seek time tends to be dominant in disk access times.

Regards,
Tony.
-- 
Tony Arnold <tony.arnold at manchester.ac.uk>
University of Manchester