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I have a 3 TB drive formatted with the GPT partition style. I use it for data on my Windows 7 PC. I've made the drive accessible via the mount point D:

My motherboard's HDD controller mode has been in RAID for some time. Recently I tried switching from RAID mode to AHCI mode in the BIOS, but after booting, the GPT partition on the 3 TB drive disappears and Windows wants to initialize it.

I'm about to migrate to a new motherboard (and therefore a new hard drive controller) and am wondering:

  • Why does Windows want to initialize my disk when I switch to from RAID to AHCI (non-RAID) mode in the BIOS?
  • How is GPT partition type related to the type of hard drive controller selected in the BIOS?
  • How do I "back up" the GPT partition data so that I can switch to AHCI mode on my existing motherboard in case my new motherboard doesn't suit my needs?

One last note: I have Regedited MSACHI's and something else's Start value to 0 from 3

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    The fact your partition isn't recognized as valid when not connected to your RAID controller is a problem quite unrelated to the partition being of the GPT type. – Twisty Impersonator Nov 28 '14 at 2:38
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    I agree. I can't replicate the issue on a GPT formatting that I made on a spare harddrive I had lying around. – paIncrease Nov 28 '14 at 4:10
  • also, "so I take it that's not normal" – paIncrease Nov 28 '14 at 5:06
  • Actually, the situation you're facing is very normal. RAID controllers by necessity must put identifying information on their member disks. Now, not all do it in a way that prohibits the disk from being read on other controllers, but it's not uncommon for some to do it this way. – Twisty Impersonator Nov 28 '14 at 13:28
  • "identifying" information-- oh right, I see why RAID controller would have to do that. Is there no standard that says "we all agreed to put it in sectors blah blah blah" so this doesn't happen? – paIncrease Nov 28 '14 at 22:23
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The problem here is that your RAID controller has written metadata to your hard drive which it understands, but another HDD controller doesn't. Out of necessity RAID controllers put identifying information on their member disks. This metadata is most often unique to the RAID controller's manufacturer and sometimes specific to the controller model or even certain controller firmware revisions. As noted in this Adaptec support article:

RAID controller manufacturer's do not use the same RAID algorithm and format. RAID table information written by one manufacturer's adapter will not be compatible with another manufacturer's adapter. Different companies implement their own unique RAID table data and RAID management software.

In some cases other hard disk controllers can read the data on a RAID member disk, especially when the disk is from a RAID 1 array created by a software-based RAID controller, but this possibility should be regarded as the exception not the rule.

Finally, RAID metadata is unrelated to and distinct from the partition type of your drive. It doesn't matter whether you're using GPT or MBR or any other partition type, the root problem it's not recognized when you change controller modes is the fact the disk is a RAID member.

Two things you can try for moving your disk from one controller to another:

  1. Contact the manufacturer of your RAID controller to inquire about options for making your drive non-RAID without losing your data
  2. Back up all of the data on your volume, move the drive to your new motherboard, format it, then restore the backup.
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    your second comment below my question helped understanding – paIncrease Nov 28 '14 at 22:21
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    Great suggestion. Answer updated. – Twisty Impersonator Nov 28 '14 at 22:29
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    Well, it’s not that unusual for “1-disk RAID” or RAID1 disks to remain readable: Most controllers write their metadata to the end of the disk, so it doesn’t interfere with the expected non-RAID layout. – Daniel B Dec 4 '14 at 19:44
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    @DanielB Agreed, although I've found drive portability to enjoy better success with software RAID controllers, but not so much with hardware controllers. However I'll edit the question to make that statement less narrow. – Twisty Impersonator Dec 4 '14 at 19:57

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