Prefetch and SSDs

[Guy Scharf]

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.

 

[Brink]

Hello Guy,

I have a older generation SSD and had to manually disable Disk Defragmenter and prefetch from running on that drive.

 

[nate42nd]

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.

 

[Brink]

Hi Nate,

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

Superfetch (Memory Prefetcher) - Vista Forums

 

[nate42nd]

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.

 

[Brink]

See if setting the value to 0 instead may help.

Superfetch - Change Preload Data - Vista Forums

 

[pparks1]

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

http://www.sevenforums.com/tutorials/5023-windows-features-turn-off.html

or

Engineering Windows 7 : Beta to RC Changes – Turning Windows Features On or Off

 

[fakeasdf]

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..

 

[nate42nd]

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.

 

[H2SO4]

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

 

[fakeasdf]

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

Oops, yes I was referring to Superfetch. But per the MSDN article "Be default, Windows 7 will disable Superfetch, ReadyBoost, as well as boot and application launch prefetching on SSDs with good random read, random write and flush performance." So I still semi wonder why they disabled superfetch, good catch there.

 

[H2SO4]

Oops, yes I was referring to Superfetch. But per the MSDN article "Be default, Windows 7 will disable Superfetch, ReadyBoost, as well as boot and application launch prefetching on SSDs with good random read, random write and flush performance." So I still semi wonder why they disabled superfetch, good catch there.

Probably to spare some wear and tear on the (limited cycle) SSD. It would cost some performance though, as an SSD still crawls compared to a RAM cache hit.

A lot of people confuse "superfetch" and "prefetch", or use them interchangeably, even in MS docs. They are not the same thing at all.

 

[nate42nd]

I don't have the two mixed up but I think I finally figured it out. I must have edited the registry wrong. It's not writing to the prefetch file now after a correct registry edit.

Is it okay to delete the prefetch files inside the folder marked "prefetch". I would think it would be fine. They are not needed.

 

[hp79]

I have the registery value set as 0 for all EnablePrefetcher / EnableSuperfetch / EnableBootTrace, and I still see activity in my Resource Monitor. Writing activity on C:\Windows\Prefetch\ReadyBoot\ReadyBoot.drl
Anyone solved this issue yet?

I have intel SSD G2 80GB. Just clean installed a week ago. I had to turn off disk defrag manually.
Windows 7 x64,

 

[First Build 10]

First Post

This is my first post and let me say first that I have and am still enjoying gathering all of the info here on this forum. I just built my first PC and I have an Intel G2 80 in mine as well and I too had to shut the defrag off manually. I did not realize PreFetch and SuperFetch were two different things...so I guess since I seem to barely use any of my 4 gig of ripjaw I should turn "Super Fetch" back on..Is this correct?

 

[hp79]

This is my first post and let me say first that I have and am still enjoying gathering all of the info here on this forum. I just built my first PC and I have an Intel G2 80 in mine as well and I too had to shut the defrag off manually. I did not realize PreFetch and SuperFetch were two different things...so I guess since I seem to barely use any of my 4 gig of ripjaw I should turn "Super Fetch" back on..Is this correct?

I wanted to keep superfetch on since my laptop has 4 GB. But then you need to have stuff like indexing (I think this is different from Windows Indexing service) turned on so your Windows knows which files to superfetch.

 

[Dave76]

Here are a couple of sites I have found many references to.

Just what tweaks are needed in win7 with SSD?

From Intels Support Community,
Question about SSD performance

A link from that site,
Windows 7 System Restore And Your SSD - IMPORTANT READING

From the above site, use caution with these suggestions, as there are many opinions on what needs to be done.
Windows 7 SSD Performance Optimization Guide

Intels SSD New Users Guide

Engineering Windows 7, Support and Q&A for Solid-State Drives


I have used the ones from the OCZ site listed first, and 'Enable write caching on the device'.
From Windows Explorer, right click your SSD, Hardware tab, select your SSD and click 'Properties' button, Policies tab, Check box 'Enable write caching on the device'.
And Check box for 'Turn off Windows write cache buffer flushing on the device', read all of this one, if you don't have a UPS you are better off not to check it.
My benchmark write scores were falling fast (SSD 3 weeks old) and this seemed to bring them back up.
I also disabled System Restore as mentioned in one of the links above to check out his theory.

 

[stereo]

Should Prefetch be disabled or not ? for SSD owners..

 

[logicearth]

No, Prefetch is not SuperFetch. Keep Prefetch. Should keep SuperFetch too.

 

[Wishmaster]

Should Prefetch be disabled or not ? for SSD owners..

Much debated around here.
It would seem some experience slowdowns, and others seem to experience a snappier system after some time.
I have had a positive experience with it left ON.

I think it really depends on how you use your PC, and what you do with it (habits etc) as to whether it will benefit you or not.
Or at least, that seems to be the case with others reports on the subject.



The best thing to do is try it both ways, On and Off, for a few days to a week and see how it works out for you.


Personally, I say leave it on.

But the bottom line is, It will not hurt the SSD. Its just fine & safe to leave On.

You very well may see some performance improvements over time, or maybe not. Just try it and see.