Windows – Should I enable or disable Prefetch/Superfetch with the new SSD

Disable ReadyBoost. Make your SSD your primary / boot drive, and / or make sure your pagefile is on it. ReadyBoost is just a secondary buffer for stuff - if your pagefile is fast enough you don't need to use ReadyBoost.

Even if you can't make the SSD your boot drive, you can still tell Windows to use the SSD for your page file. Either way it eliminates the need for ReadyBoost.

RAPID mode gives fantastically high results for benchmarks, where the test software just basically writes out data that it rereads later on. If the RAM cache is large enough, the test will only measure the RAM speed, rather than the disk speed.

For example, the Samsung 850 EVO 2TB Review article from August 2015 gives test results from three well-known products :

ATTO

Astonishing. Previous speeds were 559MB/s Read and 537MB/s Write, and with RAPID Mode enabled we’re seeing a nearly unbelievable difference at 3555MB/s Read and 3723MB/s Write!

Crystal Disk Mark

More of the same here, as results here jump to an absurdly fast 6321MB/s Read and 4239MB/s Write (up from 541 / 522 stock) in the Sequential test.

AS SSD Benchmark

Another massive jump, with Sequential Read and at 3602 MB/s and 2380 MB/s, respectively (up from 520MB/s Read and 500MB/s Write in stock mode. And look at the overall score increase, from 1091 jumping up to 36568. Wow.

However, in everyday life we don't always re-read the data we have just written, so the results are vastly different.

I have found several user testimonies :

Windows 10 Forums - Samsung Magician, July 2015

Only in the synthetic tests. There is some improvement in copying large files between two SSD drives. I used to do very high cue depths work at one time and enabling rapid definitely helped. Under normal use and gameplay, cannot see any difference. I can tell you this, it doesn't hurt. Just one person's opinion.

It definitely does not help boot times. In fact the rapid service only loads during the boot process and at best, would create a minuscule delay in the boot process.

Direct X & Samsung Magician, March 2015

For benchmarking it appears good, but actually in real-world performance, just slows down your boot, adds another background process, and doesn't speed up game performance or anything majorly useful. It's a have, and personally I see little to no point in using it, other than to give a faked illusion of more performance (which happens to be more unstable as well on quite a few system, which is why they leave it disabled as default).

And the next remark :

I had issues with the Samsung magician "Rapid Mode" on, i was not able to play any of the counter strike games. They started and after a few seconds they would froze. After turning off the rapid mode, all was good.

Conclusion

Under normal everyday use, allocating up to 25% of your RAM to RAPID takes this memory away from Windows (and the same for Linux). Windows & Linux incorporate very good memory caching which I believe will better (and safer) handle everyday use. Especially as they use this RAM for more purposes than just as a disk buffer (programs, memory data etc.).

With RAPID, one also has higher chances of losing data when power is lost or when the computer crashes before a write has been completed and sent to the SSD, as RAM contents are then lost.

I would therefore not counsel using RAPID for normal computer usage.