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Re: [OM] OT--Favorite Defrag Program?

Subject: Re: [OM] OT--Favorite Defrag Program?
From: SwissPace <ian@xxxxxxxxxxxxxxxx>
Date: Wed, 15 Aug 2012 09:00:43 +0200
As someone who used to get paid for this sort of thing  (database 
performance tuning) it did make a difference, I would however agree that 
on a modern windows systems with modern large disks it would make little 
difference.  It's really amazing how much things have changed in recent 
years.

For those who want to know

this was taken from
<http://www.ibm.com/developerworks/aix/library/au-aixoptimization-disktun2/index.html>

*Figure 2. Actual storage position on the physical disk platter*
Actual storage position on the physical disk platter

As a general rule, data that is written toward its center has faster 
seek times than data written on the outer edge. This has to do with the 
density of data. Because it is more dense as it moves toward its center, 
there is actually less movement of the head. The inner edge usually has 
the slowest seek times. As a best practice, the more intensive I/O 
applications should be brought closer to the center of the physical 
volumes. Note that there are exceptions to this. Disks hold more data 
per track on the edges of the disk, not on the center. That being said, 
logical volumes being accessed sequentially should actually be placed on 
the edge for better performance. The same holds true for logical volumes 
that have Mirror Write Consistency Check (MWCC) turned on. This is 
because the MWCC sector is on the edge of the disk and not at the center 
of it, which relates to the intra-disk policy of logical volumes.

Let's discuss another important concept referred to as the inter-disk 
policy of logical volumes. The inter-disk policy defines the number of 
disks on which the physical partitions of a logical volume actually 
resides. The general rule is that the minimum policy provides the 
greatest reliably and availability, and the maximum policy improves 
performance. Simply put, the more drives that data is spread on, the 
better the performance. Some other best practices include: allocating 
intensive logical volumes to separate physical volumes, defining the 
logical volumes to the maximum size you need, and placing logical 
volumes that are frequently used close together. This is why it is so 
important to know your data prior to configuring your systems so that 
you can create policies that make sense from the start.



On 14/08/2012 21:33, Jim Nichols wrote:
> Hi Chuck,
>
> With modern, large drives, I have seen no improvements in the rare occasions
> I have run a defrag program.  And, with the increase in drive capacities, it
> would take forever to complete a defrag effort.  I agree, snake oil!
>
>

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