AHCI, can someone explain?

[Jonathan_King]

After some Google searching, I think I need a dumbed-down explanation: what the heck is AHCI? Is it a desirable setting?

 

[kegobeer]

AHCI (Advanced Host Controller Interface) allows you to hot swap drives. It also allows for native command queuing, which allows a drive to accept multiple commands at once, and also rearrange those commands to optimize performance. If you plan on hot swapping drives, it's something you should consider. Since it can also allow a drive to accept more than one command at a time, it can increase storage speed. If your system supports AHCI, and your drives support native command queuing, I suggest enabling it.

 

[Qdos]

Doesn't get any dumber than Wiki

 

[Jonathan_King]

Now I see people here saying that in order to switch, you need to do a clean install. What does anyone think about this?

 

[kegobeer]

Doesn't get any dumber than Wiki

Except that the wiki entry doesn't actually bother to explain the concepts of NCQ or hot plug. That particular entry is pretty messy and would benefit from adding the actual explanations for the important components into the AHCI entry.

 

[Qdos]

Doesn't get any dumber than Wiki

Except that the wiki entry doesn't actually bother to explain the concepts of NCQ or hot plug. That particular entry is pretty messy and would benefit from adding the actual explanations for the important components into the AHCI entry.

That was precisely why, in the context of dumb, I posted the link

 

[kegobeer]

Now I see people here saying that in order to switch, you need to do a clean install. What does anyone think about this?

Personally, I'd opt for a reinstall. I scanned that thread, and with the differences between chipsets, the lack of a proper reg file for certain chipsets, etc, it would probably be faster to just back everything up, switch to AHCI, and then do a clean install. Plus, that's a thread for XP - I wouldn't use it for a Windows 7 installation.

 

[kegobeer]

Doesn't get any dumber than Wiki

Except that the wiki entry doesn't actually bother to explain the concepts of NCQ or hot plug. That particular entry is pretty messy and would benefit from adding the actual explanations for the important components into the AHCI entry.

That was precisely why, in the context of dumb, I posted the link

Ah, I totally didn't get that. It's been a loooooooong day...

 

[Jonathan_King]

Now I see people here saying that in order to switch, you need to do a clean install. What does anyone think about this?

Personally, I'd opt for a reinstall. I scanned that thread, and with the differences between chipsets, the lack of a proper reg file for certain chipsets, etc, it would probably be faster to just back everything up, switch to AHCI, and then do a clean install.

Thank you for your input. I will wait and get a few more responses, but your post had been duly noted.

 

[gregrocker]

Kegger can you enlighten us on what would make a RAID config worthwhile for Windows 7 since we are getting many problems with 7 install to RAID. Supposedly Intel suggests RAID config for AHCI (in the Wiki). How would that work?

Dude yesterday with SATA had IDE enabled but found AHCI choice in BIOS, then turned out AHCI driver was on mobo CD which he loaded into installer and fixed stall.

Should we even bother trying for AHCI if it is not in BIOS menu? Another way to enable it on mobo?

 

[Qdos]

Nothing wrong with adding the drivers post W7 install, however it's impossible to speculate whether updates or any other aspects of functionality would be as per normal if you installed using the method on the link within this thread.

Hitting F6 early on in setup, whilst it harks back to the earliest days of SATA, does allow you to load the drivers before the OS itself - and arguably there can be no cleaner environment.

What narks me is that Microsoft couldn't be bothered to include the drivers on their DVD disks for W7, and engineer setup to optimise AHCI when suitable SATA controllers are detected as being present.

 

[ignatzatsonic]

I remember looking into it maybe 3 years ago and figuring it would do little for me, but I can't recall the details.

If an HD supports NCQ, is AHCI necessary to take advantage of it??

I have no need for RAID or hot swapping.

I completely forgot about it when I did my recent Win 7 install, so I still am without.

Any insight into the real-world difference for typical users, non-RAID?

Speed related? Security related? Minor? Very minor? Moderate?

 

[Qdos]

Big advantage is really with eSATA. You can hotswap drives, without reboots

 

[gregrocker]

Interesting AHCI=performance boost? threads:

Will enabling AHCI boost performance? - Hardware Canucks

IDE vs. AHCI - General-Storage - Storage

Does AHCI give any performance benefit - HEXUS.community discussion forums

AHCI Controllers? - Tech Support Forum

 

[bobkn]

Now I see people here saying that in order to switch, you need to do a clean install. What does anyone think about this?

http://www.sevenforums.com/installa...-bios-much-better-performance.html#post308867

If you read through the thread, you'll see the same method given for switching to AHCI without re-installing Windows. It has been a while since I tried it, but I recall that it worked.

However, I recall that there were problems switching back to IDE mode if I used the Intel AHCI drivers rather than the Microsoft ones.

 

[ignatzatsonic]

Greg:

Thanks for the links. They confirmed my 3 year old opinion. Here are the pertinent pastes from the links provided by Greg and bobkn:

If anything, in your usage scenario, you are likely to see a slight performance decrease as a result of engaging AHCI mode.

The key reason for this is that the native command queueing, assuming your drives are capable of it, fractionally increases latency, which only tends to be outweighed by the benefits of queueing in a usage scenario where there genuinely are loads of concurrent read/write requests being made.

This usually means a server of some sort. Even "power" desktop and workstation users are unlikely to be pushing the queue depths fast enough.

In most home/power/office user scenarios, the performance benefit of disabling NCQ tends to outweigh the demerit of the slower interface, hence IDE being the quicker of the two modes in the real world - and that's forgetting about the boot delay the AHCI BIOS causes.

Is there any advantage to using the AHCI controllers over the IDE Enhanced option on the Sata ports? I ran HD Tach on the drive before I switched from AHCI to IDE. I got a very small performance boost using it in IDE Enhanced mode instead of AHCI. It wasn't much, but a gain none the less.

So, is there any advantage with AHCI over IDE?

you are far better off in IDE enhanced mode which means SATA mode ............ ACHI doesnt shine unless you are running a raid array and even then raid doesnt really give much benefit at all until you get into 3 & 4 drives



From thread that BobKn referred to:


I went back and forth between AHCI being on and being off on my new box that I built in July. Honestly, with almost ever task I did and with any benchmarking tool, I didn't see any real performance gain with AHCI enabled.

Unfortuantely, with AHCI on, I do have about an 8 second delay on each boot as the storage controller initializes. And since I do boot daily, and it was costing me 8 seconds which I didn't pick back up elsewhere, I just run with AHCI disabled.

You have to use I/O bound tasks --otherwise it won't make a huge amount of difference unless you have RAID as well.

However with LARGE photoshop files and > 1 TB size disks the I/O throughput is significantly faster than with the IDE interface - and don't forget before SSD gets cheap enough for us mere mortals to use SATA-2 will be upon us.

 

[kegobeer]

Kegger can you enlighten us on what would make a RAID config worthwhile for Windows 7 since we are getting many problems with 7 install to RAID. Supposedly Intel suggests RAID config for AHCI (in the Wiki). How would that work?

Dude yesterday with SATA had IDE enabled but found AHCI choice in BIOS, then turned out AHCI driver was on mobo CD which he loaded into installer and fixed stall.

Should we even bother trying for AHCI if it is not in BIOS menu? Another way to enable it on mobo?

Nope. I don't see the need for a RAID configuration for the average home user. If someone is looking for a speed increase, I believe the average SATA II drive is on par with a RAID array, with a lot less hassle. That's my opinion, and I'm sure others will weigh in with an opposing view.

The actual Intel documents I've read didn't mention the need for RAID - AHCI just enables advanced SATA features like hot plug and NCQ. And, the only way AHCI will appear in the BIOS is if the motherboard supports AHCI. So, if a user has the ability to use AHCI, and has a drive that will utilize NCQ, then I would recommend enabling SATA and AHCI, but stay away from RAID.

 

[seekermeister]

The only thing that I know about this, is that with the motherboard that I currently have, that I have to choose between AHCI or RAID, but not both at the same time.

 

[gregrocker]

Here is the solution of one of the guys who had been struggling here with Win7 RAID install:

http://www.sevenforums.com/installation-setup/44866-my-windows-7-install.html#post426808

 

[Tepid]

When you select AHCI,, you are also selecting RAID. AHCI is a RAID function. or vice versa.

Uses of RAID,,, if not striping several drives for speed (which you can get using 3+ drives), you can also mirror for redundancy, and yes, It saved us about 300M of wife's family pictures, our MP3 library, among a ton of other things, which would all be gone now. So, yes, there are practical home uses for RAID.

I recommend at least, 1 drive for the OS and 2 set up as a RAID mirror for data, and then also an external drive for running weekly backups.

But, it all depends on how much your data means to you.

There are 2 kinds of computer users in the world.....
Those who have lost data and those who will lose data.

The choice is yours.


Edit*** don't know why I wrote the viceversa,, cause that is actually wrong. RAID is RAID and AHCI is RAID, but RAID is not AHCI.