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Windows 7: Prefetch and SSDs


19 Oct 2009   #1

Win 7-32, XP Pro-32
 
 
Prefetch and SSDs

My understanding from reading the MSDN blog was that prefetch and defrag were to be disabled for SSDs with "good performance." I have a second generation Intel X25-M 80GB as my boot drive which I believe qualifies as a "good performing" SSD.

I do see that defrag is disabled for my SSD (C: drive). However, the c:\windows\prefetch folder is fully populated. And the registry entry HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters\EnablePrefetcher is set to 3, which seems to mean "enable all."

Does anyone know why prefetch is enabled? Is this happening for everyone?

I am running RTM from TechNet with all updates applied.


My System SpecsSystem Spec
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19 Oct 2009   #2
Microsoft MVP

64-bit Windows 8.1 Enterprise
 
 

Hello Guy,

I have a older generation SSD and had to manually disable Disk Defragmenter and prefetch from running on that drive.
My System SpecsSystem Spec
20 Oct 2009   #3

Windows 7 Professional x64
 
 

This same thing is happening to me also. I have even set the registry key you noted to "0" and it STILL writes to the prefetch folder. I can't seem to figure this one out. I you have any suggestions Brink. That is the one thing that has me baffled.

In resource monitor it says something like "readyboot.ecl" or something.
My System SpecsSystem Spec
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20 Oct 2009   #4
Microsoft MVP

64-bit Windows 8.1 Enterprise
 
 

Hi Nate,

You could also disable the "Superfetch" service to stop it.

Superfetch (Memory Prefetcher) - Vista Forums
My System SpecsSystem Spec
20 Oct 2009   #5

Windows 7 Professional x64
 
 

I did that too but I continue to get the prefetch writes. I have asked this question on the Patriot forums and received no answer there. I think I am missing something. It will be okay I'm sure. I just like to figure these things out. haha

I will try it again and do everything you say in the tutorial again. Maybe I forgot to hit "stop" or something.
My System SpecsSystem Spec
20 Oct 2009   #6
Microsoft MVP

64-bit Windows 8.1 Enterprise
 
 

See if setting the value to 0 instead may help.

Superfetch - Change Preload Data - Vista Forums
My System SpecsSystem Spec
20 Oct 2009   #7

Windows 7 Ultimate x64
 
 

Try going in and turning off the Prefetch feature following the link here:

Windows Features - Turn On or Off

or

Engineering Windows 7 : Beta to RC Changes €“ Turning Windows Features On or Off
My System SpecsSystem Spec
20 Oct 2009   #8

Win 7 Pro x64 x 3, Win 7 Pro x86, Ubuntu 9.04
 
 

This is good information to know! I'm surprised superfetch is disabled tho, it seems even with the rocking speeds of SSD's, RAM speeds still destroy them when it comes to transfer rates, especially due to the SATA 2 controller limits. I guess maybe it's a minuscule gain and not worth letting your system worry about it? I dunno..
My System SpecsSystem Spec
20 Oct 2009   #9

Windows 7 Professional x64
 
 

I gave up a few weeks ago. I have a 10MB prefetch folder and one day I will get it solved. Thanks for the links pparks.

The answer to the original question is make that value 0. It seems to work for most people Guy Scharf.

I am starting to wonder if I just have not deleted the existing files in that folder because I can't see it writing to it now......maybe that DOES work.
My System SpecsSystem Spec
20 Oct 2009   #10

Win7x64
 
 

Quote   Quote: Originally Posted by fakeasdf View Post
This is good information to know! I'm surprised prefetch is disabled tho, it seems even with the rocking speeds of SSD's, RAM speeds still destroy them when it comes to transfer rates, especially due to the SATA 2 controller limits. I guess maybe it's a minuscule gain and not worth letting your system worry about it? I dunno..
Prefetch is not the same thing as superfetch. I'm guessing you're thinking of the latter.

Prefetch is essentially a disk optimisation mechanism. It monitors which fragments of which executable files are commonly used together, and then causes them to be laid out next to each other on disk, even if it means the layout doesn't make much sense to the casual observer.

(Incidentally, that's why 3rd-party non-prefetch-aware disk defraggers can sometimes mess up the on-disk layout and slow things down, but that's a different story.)

SSDs have extremely low seek times and no rotational delay, so access times are uniform irrespective of "where" on the disk a particular fragment is to be found; in fact, "where" is almost non-sensical when using an SSD. Prefetch therefore loses its main raison d'etre. (There is another one, but it's minor and too involved to explain.)

Superfetch is a predictive RAM pre-population thing. Instead of having unassigned RAM stay totally useless, superfetch fills it with stuff it thinks might be useful in the near future, based on past observation of that machine's usage patterns. No direct link to the disk or to prefetch. They just like using silly names
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 Prefetch and SSDs




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