Is it necessary to enable AHCI for better performance using SSD?

[d_chew]

I recently migrated my Windows 7 64bit OS in my DELL latitude E4310 laptop from HDD to SSD (Samsung EVO 840 250GB).

I used crystaldiskmark to benchmark the SSD performance. I am getting about 240MB/s for read and write in the sequential test. I am expecting the results to be near 400MB/s or 500Mb/s.

I checked, the BIOS is set to use RAID as DELL's default. I tried to change to AHCI and got a blue screen during next reboot. I googled and checked many and know that it is advisable to install OS fresh. I would like to know

-if it makes a difference for installing a new fresh OS?
-Allow AHCI with new OS install?
-WIll I get closer to 400Mb/s with new OS?

Thanks.

 

[SethJPC]

No, you don't need a fresh install of your OS, ACHI is faster and you will definitely get faster read+writes. I had the same problem when changing to ACHI, you need to tell the registry how to boot with it properly, follow the steps in this link:

http://www.sevenforums.com/tutorials/61869-ahci-enable-windows-7-vista.html

or for windows 8:

http://pricklytech.wordpress.com/2014/02/04/windows-8-1-enabling-ahci-after-installing-windows/

 

[InvalidError]

You need AHCI for full NCQ and TRIM support, which are "kind of" critical for optimal SSD operation.

Without AHCI, the drive operates in legacy mode where it behaves like a dumb old PATA drive apart from the faster burst data rates.

 

[k1114]

You can't get to 400MB/s on sata 2 and max sequential isn't important for most people.

 

[d_chew]

I have tried the registry method before and double checked several times to ensure no mistake. However still no luck. I booted with AHCI. Got BSOD as usual. I am thinking of reinstalling OS seriously.

No, you don't need a fresh install of your OS, ACHI is faster and you will definitely get faster read+writes. I had the same problem when changing to ACHI, you need to tell the registry how to boot with it properly, follow the steps in this link:

http://www.sevenforums.com/tutorials/61869-ahci-enable-windows-7-vista.html

or for windows 8:

http://pricklytech.wordpress.com/2014/02/04/windows-8-1-enabling-ahci-after-installing-windows/

 

[d_chew]

This is what I did to resolve the issue. Very close to SethJPC's solution. ie changing values in the registry. Apart from the msahci & iaStorV, I also made changes to "atapi".

Locate the following keys and change the DWORD “Start” from “3” to “0”:
atapi

Credit to this post:
http://esupport.trendmicro.com/solution/en-US/1096453.aspx

I have since managed to switch from RAID to AHCI in BIOS and booted successfully. I run a test with AS SSD benchmark. The score was impressive with an improvement from 542 to 948 score.