Hi Phil,
I thought the same, but this is from the app’s help file:
Why Defragment?
It is often asserted that defragmentation (or disk optimisation) is not a good
idea on systems using Apple’s HFS+ filesystem. The main reasons given for this
are:
• HFS+ is very much better at keeping files defragmented than other
common filesystems.
• Advanced features of HFS+ can easily be disrupted by a
defragmentation tool that does not support them, resulting in decreased
performance.
• HFS+ includes its own defragmentation support.
• There is a risk associated with defragmentation.
While these arguments are certainly valid, they are not the whole story.
iDefrag, unlike older defragmenters, does know about and support the advanced
features of HFS+ such as the Hot Zone and the adaptive hot file clustering
support introduced in Mac OS X 10.3. Not only does it avoid disrupting them,
but it is capable of fixing disruption caused by other software.
Likewise, the built-in automatic defragmentation support in HFS+ is somewhat
limited in scope; in order for it to trigger:
• The filesystem must be journaled.
• The file must be under 20MB in size.
• It must have at least eight fragments.
• It must not have been modified within the past minute.
• The system must have been up for at least three minutes.
• The file must not currently be in use by any program.
• A program must open the file.
Sensible arguments for occasional optimisation of your disk include:
• HFS+ is not very good at keeping free space contiguous, which can, in
turn, lead to large files becoming very fragmented and can also cause problems
for the virtual memory subsystem on Mac OS X.
• Older versions of the Mac OS are not themselves aware of the Hot Zone
policy and may disrupt its performance.
• HFS+ uses B-Tree index files to hold information about the
filesystem. If a large number of files are placed on a disk, the filesystem may
have to enlarge these B-Tree structures; however, there is no built-in
mechanism to shrink them again once the files are deleted, so the space taken
up by these files has been lost.
• While HFS+ is good at keeping individual files defragmented, software
updates may result in files that are components of the same piece of software
being scattered across the disk, leading to increased start-up times both for
Mac OS X itself and for applications software. This is a form of fragmentation
that is typically overlooked.
• Defragmenting disk images can be helpful. It may allow them to be
more heavily compressed, and it also prevents unnecessary seeking if they are
burned to a CD/DVD (where seeks are especially expensive).
• Some specific usage patterns may cause fragmentation despite features
of HFS+ that are designed to avoid it.
We do not recommend very frequent optimisation of your disk; optimisation can
take a long time, particularly with larger disks, far outweighing the benefits
that are likely to be obtained by (say) a weekly optimisation regime.
Hope that sheds some extra light.
Stephen
"What we see is partly a function of what we believe we see: our truth is
constrained by the times in which we live" - Richard Fortey,
> On 15 Jan 2016, at 17:05, Phil Ward <[email protected]> wrote:
>
> Hmm, that’s interesting. Fo some reason I thought disc defragging was a thing
> of the past and that OS X does it automatically. Did I dream that?
>
> P
>
> ----
> Phil Ward
>
> Skype: aphilw
> E: [email protected]
>
> W: philward.biz
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>
> • Freelance writer and product designer.
> • Contributor to Sound on Sound magazine.
> • UK distributor for Veillette Guitars. www.veilletteguitars.com.
>
>> On 15 Jan 2016, at 17:01, [email protected] wrote:
>>
>> Hi all,
>>
>> I found my Mac to be getting very slow of late, just to login and launch
>> apps and open documents was becoming tedious and so bought a defragmenter to
>> see if it would help.
>>
>> I bought iDefrag which I ran last week and it seems to have produced
>> impressive results. Some things take about the same amount of time as before
>> but most things are quicker, and some dramatically so - system preferences
>> for example now takes two seconds to appear whereas before it would take
>> about 15!
>>
>> I reckoned that having a mid-2011 iMac (500GB disk and 12MB RAM) that had
>> had three OS upgrades (I think) and any number of point upgrades to the OS
>> along was probably in a messy state and indeed the fragmentation map seemed
>> to be red everywhere (bad news).
>>
>> The app is about £27 and is cheap speedup in my view. They say on their site
>> ( http://coriolis-systems.com/iDefrag/ ) that it’s no help on an SSD drive.
>>
>> Just thought you may like to know.
>>
>>
>> Cheers,
>>
>> Stephen
>>
>>
>>
>> BBC news November 2006: "China has some of the world's most polluted rivers,
>> and is accused of overlooking the protection of the environment to develop
>> its economy."
>>
>> Appalling. We'd never do anything like that in the West...
>>
>>
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> ----
> Phil Ward
>
> Skype: aphilw
> E: [email protected]
>
> W: philward.biz
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> W: soundcloud.com/philberish
> W: peggysdiaries.wordpress.com
>
> • Freelance writer and product designer.
> • Contributor to Sound on Sound magazine.
> • UK distributor for Veillette Guitars. www.veilletteguitars.com.
>
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