So, it's indeed possible to replace the disks of a bootable RAID-1 volume on a RocketRaid 1820A card. The box in question is running Windows 2003 server. It has hot-swap SATA drive bays. This makes it easy- if you don't have bays it becomes a lot more challenging. Before I go on, of course, make sure you back your stuff up. I didn't, but you should. I'm not responsible for your data, job, etc...

So, here we go:

• Have your two new bigger drives ready. Make sure they were wiped clean before you go on.
• Boot up your box if it's not running already.
• Start the RAID management application. Do a verify/rebuild on your RAID-1 just to make sure everything is clean and ready to go.
• Pop out one of the RAID-1 disks. The computer will start beeping and complain that the disk is missing. Dismiss the warning. Keep this disk safe, as you can boot from it later if things go horribly wrong.
• Insert one of the new disks in the hole left by that disk.
• The system should notify you that a new disk was plugged in. It should ask if you want to rebuild the array onto it. Do that.
• Wait for the rebuild to complete. Verify it afterward if you're really paranoid.
• Shut the system down.
• Pop out the other original disk, leaving the one new disk as the sole member of the RAID-1.
• Boot the box. The HPT BIOS should complain about the RAID-1 being broken. A pop-up should appear.
• Select DESTROY to remove the mirror relationship. The box should reboot.
• It should then boot up into Windows on the standalone drive. This is key, because as a standalone drive, you'll see the full capacity!
• Enter Disk Management to create your new partition(s) and volumes in the unused space on the boot disk.
• Start the RAID management application.
• Insert the other new disk. It'll notify you that a new disk was inserted.
• Select create array. Select RAID-1. Then choose the disk you booted from first, the blank disk second. This is important, if you do it backwards, you'll erase the one good boot disk! Select DUPLICATE.
• It'll now make a copy of the source disk onto the mirror disk. This may take some time. Get some coffee.
• When it's done, go ahead and rename the array if you want.
• Reboot the box to make sure it works.

That's it! I did this to replace a 40GB RAID-1 that was getting ancient with some newer 200GB disks, and it worked great for me.

Hope this was helpful!