A quick tip for those who might be moving from a mobo-enabled hardware RAID approach to a software RAID approach as enabled by Windows 7.  The particular use case I’ll describe here is for RAID 1 (Mirroring).  A typical scenario could be:

1. You’ve got a mobo that has a hardware feature for enabling SATA (or other) RAID.  You had decided to use RAID Level 1 (mirroring) to enable redundancy of data across disks using this mobo-based embedded RAID.  You believed that this would provide to you the ability to recover quickly in the event of a single disk loss.  Note: RAID 1 is NOT a backup solution.
2. You’ve had a RAID warning on one of the disks.  You reboot and discover that the assigned array drive doesn’t contain all of your recent work.  This could be because of the hardware vendor’s implementation of write behavior, caching, etc. You disable RAID completely in the BIOS (or via driver configuration), and enable the other drive (mount it online) as your former RAID volume letter, and discover your data is there.  Maybe it was just a mobo driver problem?  Likely.  I’ve wrestled with mobo-enabled RAID solutions for years now only to finally realize they just don’t work as advertised.  If you need real hardware RAID, go to Adaptec.
3. In a sigh of relief upon booting your computer and seeing your data, you decide that you should now really understand how to recover the mirror in the event of various types of failures, and start researching what really can happen when an embedded mobo RAID solution blows up.  You essentially discover you have to have a replacement mobo and drivers handy.
4. Realizing this might not be realistic, you remember that Windows has software RAID features.  You start researching, and find out that in the event of a mobo failure, you can (in theory) take your Windows software RAID drives to a replaced machine.  You also learn that software RAID has improved significantly recently and you may only suffer a very small penalty on write operations, which are a minority of the operations for most non-server applications.
5. You fire up Windows (in my case, Windows 7 Ultimate 64-bit), and launch Disk Management.  What next?

At this point, assuming there aren’t actually any hardware issues with your drives, you can ensure that your good drive is mounted as your former RAID volume letter.  Take the second drive and wipe it, but only if you have backups of your data!

Now, you go to mirror the second drive with the first (that has your data).  How to do this?  In Disk Management, you right-click on the drive (in the right-hand space representation) of the drive that has your data, and click ‘Add Mirror’, like so:

Except, you discover, as is highlighted above, that Add Mirror is greyed out, and disabled.  What gives!?

The solution was not trivial, but worked for me:

• You must ensure that your secondary drive, the one you’ll be creating a mirror of your first drive with, is ‘Unallocated’ (Delete Volume).
• If that doesn’t work, then perform a ‘Shrink Volume’ command on the drive that contains your data.  Choose a very small shrink amount, such as 512MB.  You should have much more than this free.  This operation may take awhile.  Go grab a beer – or a scotch, or three.
• When that operation is complete, you’ll be left with 512MB of unallocated space.  This of course is simply annoying, I want to be able to use all the space I have!  So…
• Now perform an ‘Extend Volume’ command on the drive that contains your data.  Extend it by the maximum allowable amount.

Voilà!  Now right-clicking the drive that has your data on it reveals the ‘Add Mirror’ command to be enabled for you to extend your existing drive onto the second drive, as a RAID 1 Mirror.  This will invoke a resynchronization, which will take some time.  Grab more beer/scotch, or go to bed and let the drives synch overnight.

Please, one caveat: YMMV on this.  There are simply too many different drive combinations, OS versions, etc. for me to comment on all of them.  However, this worked out nicely for me, I hope this helps someone! 

Happy New Year 2011!