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Some see things as they are, and ask "Why?"   I dream things that never were, and ask "Why Not".  
Robert F. Kennedy

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Thursday, May 5, 2011

I've Got a Tiger in my Tank!

No, this is not an Esso/Exxon commercial.  (Of course, you do realize that I am severely dating myself with that reference!)

Neither is this a commercial for Mac's OS-X.

Instead, this article is about a little known - and probably even less often used - SATA drive mode called AHCI which stands for "Advanced Host Controller Interface".  There's even a nice Wikipedia article about it that goes into all the gory details if you're interested.

AHCI supports all kinds of fun features like the ones listed below.
(Taken from the AHCI Spec - Rev 1.3, available on IBM's web site here.)

AHCI specifies the following features:
• Support for 32 ports
• 64-bit addressing
• Elimination of Master / Slave Handling
• Large LBA support
• Hot Plug
• Power Management
• HW Assisted Native Command Queuing
• Staggered Spin-up
• Cold device presence detect
• Serial ATA superset registers
• Activity LED generation
• Port Multiplier
The support for port multipliers is important, especially if you want to get a nice shiny new External SATA RAID box - as most of them require port-multiplier support nowadays.

The large LBA support is especially important because it allows you to connect HUGE drives to the system - and the staggered spin up helps avoid smoking your computer's power supply when you fire up that monster 32 drive array!  Though you would hope that any array that size would have its own dedicated power supply, right?

There are - as always - a couple of flies in the ointment:
  • Many self-booting utilities, (like Apricorn's hard drive backup/cloning software), haven't even thought of AHCI, let alone support it.
  • If you're running anything older than Vista or a Hot Smokin' Linux Kernel, fuggedaboutit!  Don't even try.
  • If you ARE running Vista or better, (trust me, anything you might be running is much better than Vista!), or a Hot Smokin' Linux Kernel - and didn't install with AHCI enabled at initial install time - when you change to AHCI and reboot, your computer is liable to look at you with a puzzled expression and ask "What's a Cubit?"
I have no idea how to mitigate this in Linux as I have neither tried it, nor have I researched it.  On the other hand, Microsoft has already released a Knowledge Base Article describing the registry hack you must do - before making the switch - to clue your computer in on what's about to happen.

All in all, especially as multi-petabyte RAID arrays become common attachments to the average X-BOX game console, AHCI is going to become increasingly important.

What say ye?



  1. nice post dear blogger

  2. You got me here, I was expecting a photo of a tiger in your back yard's tank.


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