AHCI and SSD's

#1
According to a bulletin on the OCZ site;

AHCI


AHCI is not official supported on OCZ SSDs and may under some circumstances affect performance,
specifically during windows installation. Enabling AHCI can result in higher performance in synthetic
benchmarks for SSDs and HDDs alike, but can cause hang-ups and intermittent freezes in SSDs since it allows multiple access requests to compete for a drive that is not made to address re-ordering of commands in the queue. We recommend AHCI is set to disabled in both Windows and in the BIOS.
Native Command Queuing greatly increases the performance of standard rotational drives but it has no bearing on SSDs.

With AHCI on; my drive score went from 7.1 to 7.3, but my computer became unusable from the same symptoms quoted in the bulletin.
As for my overall WPI score; it is limited to 4.4 because of the over emphasis on Aero Performance. I have not invested in a graphics card, nor do I need to. If not for the low Aero score I would rate a 5.9; My processor gets a 6.7 and memory, a 5.9 - I'll upgrade the RAM some time soon.
 


loathe

New Member
#2
I have my Vertex 60GB configured to AHCI and my WIE is 7.3. I have no problems with lockups on my SSD, its nothing but bliss. I do use the native Windows driver though as the Intel one slows wiper down to a crawl for me. But in AHCI with newest Intel driver, I get by far the highest benchmark results.
Sometimes when I access my hard drives, there is a slight lag, but I always thought it was because the drives had to start spinning back up to speed as they are not always being accessed. Maybe its because Im in AHCI.

Are you using a first or second generation SSD? Thats an interesting bit of text, hadnt seen that before. I guess Ive always just used AHCI rather the IDE mode.
 


#3
Ssd & ahci

My SSD is also a Vertex 60 with the latest firmware. Sluggish behavior was one of the symptoms I observed using AHCI.
Now that I have reverted to IDE Mode, the SSD is instantly responsive. The slightly higher (+0.2) performance index using AHCI is a false indicator of real performance. In this case, real-world performance actually suffers considerably.
As recommended, I also re-set the registry setting for AHCI: Start Value = 3 (disable). Remember that this setting needs to be "0" (enable) if you want to set the BIOS to AHCI mode. Otherwise, you get the dreaded "Blue Screen Of Death". :eek: *

*Reference: Microsoft kb922976 Error message when you start a Windows 7 or Windows Vista-based computer after you change the SATA mode of the boot drive: "STOP 0x0000007B INACCESSABLE_BOOT_DEVICE"
 


loathe

New Member
#4
Out of interest, what southbridge are you using? I have a ICH9R and dont have the same problem as you. I am however going to run in IDE mode for a while to see if I can notice a difference. You are talking about this key yeh?
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci

*EDIT* I just looked at your link.

Thanks for the tip.
 


Last edited:
#5
Ssd & ahci

My motherboard uses the nVidia 8200 chipset.

Computer is a Shuttle SN7800 Kit with:
AMD Phenom 8750 Triple Core 2.4GHz @2.9GHz
4GB DDR2 800 RAM
OCZ Vertex 60 SSD SATA
WD 250GB HDD SATA
Sony CD/DVD Drive
Logitech DiNovo-Edge Keyboard
Samsung 2443 LCD Monitor

And yes, that is the correct registry address.
 


#6
Ahci

I will drop this discussion after this post.
As far as I can tell, AHCI allows NCQ (Native Command Queing) and hot swap. That's all!
I found this post on another forum and it backs up the bulletin from OCZ. ie. it's of no use for SSD.
If you new what NCQ did you would know that there is no point in enabling NCQ on an SSD... if its even possible.

NCQ is an intelligent way of ordering where the head goes in a hard drive. If you ask it to go to three places, it won't always do them in the order you ask, but will do them in an order which requires the least head movement.

Because SSD's have a less than 1millisecond access time due to the fact that they don't have heads moving over rotating disks, NCQ is slightly pointless.

Let me also advise that NCQ is actually designed for server environments, where it isn't always important that the current operation gets done quickly, more that all of them get done in the least amount of time possible. It won't make your hard drive faster at normal windows tasks or for gaming.
 


#7
Stop: 0X0000007B

During the setup after restarting the system the following error: 0x0000007B (0x80D86DB58, 0xC0000034, 0x00000000, 0x00000000) appears in a blue screen.
Has anybodý an idea?

Thank you.

Ludwig
 


#8
7B BSOD is commonly seen when the Sata HDD controllers are not loading up correctly, or an OS was installed with HDD running in IDE mode but then changed to SATA/AHCI mode afterwards (and vice versa). I would try changing the mode you are running your HDD in within the BIOS.
 


This website is not affiliated, owned, or endorsed by Microsoft Corporation. It is a member of the Microsoft Partner Program.