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I have ordered a OCZ SSD and it will be the first that I have installed. In prepping for it's arrival and install, I reviewed MSI web site to be sure I do as much right the first time as possible. On their site MSI HQ Usere to user faq they note the following:

AHCI and SSDs

Typically, many hardware review sites, as well as SSD manufacturers are recommending that AHCI mode is used with SSD drives. However, we have run our own tests here in the forum, and we believe this is misleading, only where SSD drives are used independently (ie not in a RAID array).

AHCI mode as previously explained enables NCQ (native command queuing) which is really not required for SSDs as they do not need optimizing in this way as there is no physical movement of heads or platters. In many cases, it can actually hinder SSD performance, and even reduce the lifetime of your SSD.

In many of the answered questions and directions here on SU, enabling AHCI has been strongly implied. My goal is to set the drive up for max performance and longest life. This MSI statement has moved me to inquire with you.

So the question is, use AHCI or not and why?

I have a MSI 790FX-GD90, 4 GB ram, running windows home premium 64.

EDIT: I should add that If this all goes well, I intend on getting a second SSD for RAID setup.

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I would have imagined NCQ benefits SSDs, as SSDs have multiple NANDs - if a NAND holding certain LBAs is being erased or written, a different NAND containing different LBAs could be read from, and I would have thought NCQ would be beneficial in allowing the SSD to return the second LBA first. Isn't that what NCQ does? Not terribly sure though. –  ultrasawblade Aug 25 '12 at 17:11
    
I have some invetigating to do and good points. I have yet to look at OCZ or other independent results/tests yet based on MSI's observations. –  Carl B Aug 26 '12 at 3:22
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I get the distinct feeling whoever wrote that FAQ is just blindly quoting wikipedia without any understanding. ultrasawblade's description of the value of NCQ for SSDs is spot on. In fact, NCQ makes a much bigger difference for SSDs than it ever did for hard drives. –  Mr Alpha Aug 26 '12 at 15:37
    
@Mr Alpha good note. The one part I did notice in the first part of the quote is "SSD drives are used independently (ie not in a RAID array)." So might this be more focused on running SSDs in Raid? –  Carl B Aug 27 '12 at 21:25
    
@CarlB The value of NCQ is irrespective of whether the drives are in a RAID or not. But if you are going to RAID the drives the question is moot. RAID mode is AHCI mode with the RAID capabilities tacked on top. –  Mr Alpha Aug 28 '12 at 9:13

2 Answers 2

up vote 5 down vote accepted

I would enable AHCI, because:

  • It often boosts performance (your SSD might be an exception, but if you run a SSD and a HDD then the HDD will get some boost).
  • It offers additional features (e.g. hot-plugging drives).
  • It is enabled just about everywhere else and having a system unexpectedly in a ancient compatibility mode would throw me for a loop. I realise this might be a personal thing.

Reasons not to use AHCI:

  • You use windows XP (now nearly 12 years old) and do not want load additional drivers during installation. (XP does not understand AHCI. It need a floppy with drivers for that).
  • If you have the rare situation where one specific disk is slower with AHCI. In the part you quoted it merely states that it can actually hinder performance. Not that it does, nor that it is significant. Therefor I would test with both AHCI enabled and with AHCI disabled.

Note that if you run Windows 7 (or Linux or BSD), then you can change betyween AHCI and IDE-compatible mode without reinstalling. You do need to enable a service in Windows 7.

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+1 for your comment. What service would you be refering to in win 7? –  Carl B Aug 25 '12 at 20:30
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The msAHCI service. If windows 7 is installed as IDE mode then you can use regedit and go to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\msahci. Set the value of the start dword to 0. Then shut windows down, go to the BIOS, enable AHCI ( Not the other way around ). –  Hennes Aug 25 '12 at 23:52
    
up arrow for the added comment. Also to your point on the quote (about performance impact), I am more concerned about the "even reduce the lifetime" part as this thing should scream compared to a platter drive. –  Carl B Aug 26 '12 at 3:15
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I can't find good sources on the net, but my assumption is that lifetime problems do exist for first generation SSDs. But modern SSDs seem fine with heavy use, even if daily for five or more years. AFter that they get replaced anyway. –  Hennes Aug 26 '12 at 11:33

I tested my 256G SSD both with IDE mode and AHCI mode (As an SSD Benchmark). It has a large boost in sequential read (338 MB/s to 488 MB/s), a dramatic boost in 64-threads-4k-read (22.8 MB/s to 175 MB/s) and 64-thread-4k-write (96 to 179). Sequential write increase a little from 255 MB/s to 269 MB/s and access time are not improved so much but also see a little increase.

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When using the SSD to host the OS the change in 4 KB reads is probably the most significant. Not that much needs for large serial reads on an OS drive. Also Wow, I expect an increase. But from 22.8 MB/sec to 175 MB/sec is a huge difference. –  Hennes Mar 8 '13 at 16:34

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