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Windows 7: Prefetch and SSDs

21 Oct 2009   #11
fakeasdf

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

Quote   Quote: Originally Posted by H2SO4 View Post
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
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.


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21 Oct 2009   #12
H2SO4

Win7x64
 
 

Quote   Quote: Originally Posted by fakeasdf View Post
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.
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21 Oct 2009   #13
nate42nd

Windows 7 Professional x64
 
 

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.
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19 May 2010   #14
hp79

Windows 7 x64
 
 

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,
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19 May 2010   #15
First Build 10

Windows 7
 
 
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?
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20 May 2010   #16
hp79

Windows 7 x64
 
 

Quote   Quote: Originally Posted by First Build 10 View 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?
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.
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21 May 2010   #17
Dave76

Microsoft Community Contributor Award Recipient

Windows 7 Ult x64 - SP1/ Windows 8 Pro x64
 
 

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.
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07 Jul 2011   #18
stereo

Windows 7 Ultimate x64
 
 

Should Prefetch be disabled or not ? for SSD owners..
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07 Jul 2011   #19
logicearth

Windows 10 Pro (x64)
 
 

No, Prefetch is not SuperFetch. Keep Prefetch. Should keep SuperFetch too.
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07 Jul 2011   #20
Wishmaster

Windows 7 Home Premium 64bit
 
 

Quote   Quote: Originally Posted by stereo View Post
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.
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