Prefetch and SSDs

Microsoft did some extensive testing on the then current SSDs for the Windows 7 release. They determined that the gain from Superfetch and Prefetch was, at best, a slight positive to neutral improvement when using SSDs. The thought was to disable these features and free the processor of "un-necessary" overhead and thus increase the NET gain of a PC as a whole. This applies to the older SSDs. The newer SSDs are substantially faster with higher transfer rates so if you do use a SSD (or more), you will improve throughput by disabling Superfetch and Prefetch. This is a general statement as there are always exceptions. For instance, some motherboard controllers will reach near maximum throughput on a SATAII (3GB/s) interface much less the SATAIII (6Gb/s) standard. (To wit: Marvel controllers.) In cases like this or with sub-par SSDs, it's better to leave Superfetch and Prefetch enabled.

Disabling De-fragmentation is a different reason all together. That is done for longevity of the SSD.

Carwiz,

You wont increase throughput by disabling prefetch or superfetch. The only time superfetch or prefetch affects your systems are

1. When it keeps track of what programs you open and what files you use to boot. This amounts to nothing.
2. Briefly when you log in for superfetch as it loads frequently accessed programs into memory.

It has nothing to with nor affects your SSD throughput.I don;t understand what you are trying to say about SATA 2.0 vs 3.0 and what that has to do with prefetch and superfetch or what the Marvell 6Gb/s has to do with anything.

What do you mean about write caching on the SSD ?
I mean the option " Turn off Windows write-cache buffer flashing on the device"
Should be enabled or not ?

stereo said:

What do you mean about write caching on the SSD ?
I mean the option " Turn off Windows write-cache buffer flashing on the device"
Should be enabled or not ?

Windows needs to keep its filesystem in a consistent state - that means it needs to know that if it writes critical data to a disk drive, it needs to know it was actually write on the disk. When the drive has an on-board memory buffer, it will return a success to windows when it has the data in the buffer, and will write it to disk later, when the buffer gets full. If the power drops or the before the data in the disk drive's buffer gets written to disk, it will leave windows in an inconsistent state and you would have to recover or reinstall.

With write cache flushing, when windows is writing data that is critical to maintaining the consistency of the operating system, it tells tells the disk drive to write it from cache t disk immediately.

So, you should not turn this off unless your disk system has a battery backup (unlikely) or you are on a UPS that can hold power until you can shutdown cleanly. Otherwise you run the risk of corrupting the OS.

essenbe said:

Part of what carwiz was saying came from an interview with a Msft engineer on how windows 7 dealt with SSDs. They origionally designed windows to turn off Superfetch and prefetch on 1st gen. SSDs. They found that the SSD degraded and slowed down until they turned superfetch and prefetch back on. So, they left it that way. We are now in the 3rd gen. of SSDs but windows still handles them like 1st gen. Still, on most SSD websites they say turn off superfetch. I know Intel and OCZ do. With superfetch on, Intel's toolbox configuration section will turn red and tell you your system is not properly configured.

I think you might have that backwards. I think you meant that they found that the SSD degraded and slowed down until they turned superfetch and prefetch back off, not on.

I have been running my M4 SSD for a month with both fetches on. I don't even have TRIM as I am using the Marvell controller, and I have had no performance degradation whatsoever.

Cheers

Ah yes, in the context of that article what you said makes sense. The reason the turned it on for low performing first generation SSD was the same reason it is used for disk - a marked perceived improved app load time by pre-loading often used apps to memory.

But what I think they do is use the WEI to determine if the SSD is a low performer or not. If it is, a poor performer they turn superfetch and prefetch on, if not, they turn it off. So they aren't really treating all SSD like they are first generation.

However I don't think that article has any bearing on whether one should turn superfetch and prefetch on for the current generation. I still think it is better having it on for the reasons I have stated.

Cheers