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Enable RAID on the boot disk without a reinstall System
When I went to set up RAID on the boot disk on my Mac OS X box, I had trouble finding info on the net about how to do it without having to re-install the OS. Well, here is a step by step account of how I was able to accomplish this.

Read the rest of the article for the how-to -- and please read the dislcaimer before you start doing something like this to your system! These instructions also assume some Terminal knowledge...]

DISCLAIMER: I take no responsibility if you choose to follow the steps below. I make no garauntees that this will work for you, however it did work beautifully for me. You may potentially lose all of your data, so I strongly suggest making a backup copy before trying this!
  1. Install a new hard drive
  2. Boot off Mac OS X Install CD #1
  3. Install a minimal OS on the new hard disk:
    • Click 'Customize' when it asks what type of installation
    • Uncheck everything but the BSD subsystem box
    • This install takes maybe 10 minutes
  4. Reboot and hold the Option key to get the boot loader menu
  5. Boot off the new hard disk
  6. Open a terminal and su to root
  7. Run the following command: diskutil list:
    • Look for the old disk in the output, will probably be disk1
  8. Next run diskutil enableRAID mirror disk1:
    • The disk will disappear from the desktop for about 30 seconds, then re-appear
  9. At this point, I reboot the system and hold down Option while it reboots
  10. Now select the old disk to boot from
  11. Log in and open the Disk Utility app in Applications -> Utilities
  12. Select the RAID volume and the RAID tab
  13. Drag the new disk to the RAID
  14. Click Rebuild:
    • Rebuilding usually take 1-2 hours depending on the size of your disk
  15. Drink a beer as you now have a mirrored boot drive
There should be an easier way to do this. You could theoretically boot into single user mode off of the Install CD, and bypass installing the OS on the new drive. However, diskutil seems to be broken in single user mode; I believe this is a known bug.
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Enable RAID on the boot disk without a reinstall
Authored by: plink53 on Oct 18, '04 04:05:52PM

There is a faster (and easier) way to do this, especailly since you're already suggesting that the user back up their boot disk. If you backed up your boot disk to a firewire drive, then boot off that drive. Put however many drives into your desktop or server that you want, then run the normal Disk Utility routines to create a mirrored drive. This is a very quick process that doesn't require the block-by-block copying of the master disk. Once the mirror is created, copy your boot disk to this RAID set and reboot. I've used both Carbon Copy Cloner and SuperDuper to do this and it's much faster than the mirror restore.

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Enable RAID on the boot disk without a reinstall
Authored by: Han Solo on Oct 18, '04 09:42:16PM

I was under the impression that only G5 machines can boot off a software RAID. Is that correct? I'd love to implement a level 1 RAID on my MDD dual G4 with 2 internal drives — if I could still boot afterwards. ;)

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Enable RAID on the boot disk without a reinstall
Authored by: Jaharmi on May 30, '05 10:02:04PM

I'm booting a Power Mac G4 dual/450 from a mirrored RAID volume, so it can be done on lesser Macs than a Power Mac G5.

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Enable RAID on the boot disk without a reinstall
Authored by: briank on May 10, '08 09:24:26PM

It appears that the 933MHz G4 *cannot* boot from a software RAID.

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Enable RAID on the boot disk without a reinstall
Authored by: brainiacboy on Oct 19, '04 01:33:32AM

Wished I had known about these two alternatives, I have a mirrored drive setup on a G5 but I did it the hard way, repartition and reinstall. But, does Apple really only support mirroring (or striping) of entire drives? Serious server systems allow making RAID objects at the partition level which allows for a whole lot more flexibility. Is it possible to mirror say only the first partitions of two drives, leaving the other partitions as normal or for use as stripes or whatever?

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Enable RAID on the boot disk without a reinstall
Authored by: Hes Nikke on Nov 29, '04 12:33:01PM
Serious server systems allow making RAID objects at the partition level which allows for a whole lot more flexibility.

They may allow for flexibility, but they are anything but serious. One thing RAID (Redundant Array of inexpensive Disks) level 1 (AKA mirroring) likes is to have the read/write heads move in sync between all drives. When you start doing RAIP (Redundant Array of Independent Partitions) you loose the ability to keep the heads in sync, and in turn hamper your performance. A lot.

Then there is "RAID" level 0... there is nothing redundant about striping, therefor it isn't RAID, it only uses multiple disks.

vacuums do not suck. they merely provide an absence that allows other objects to take the place of what becomes absent.

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BootCD is another option
Authored by: JohnDCCIU on Mar 08, '05 01:47:06PM
There's one additional option that will let you avoid having to install OS X on the second drive, and without using single-user mode.

I instead booted from a CD that I had built using CharlesSoft's BootCD v0.6. I usually keep a CD made from BootCD around for troubleshooting anyway (i.e. running DiskWarrior before the Alsoft CD can boot a newer machine), so it wasn't extra effort in my case.

Other than that difference, I followed this procedure and it worked perfectly on three different G5s.

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safer and surer
Authored by: inviscid on Jul 05, '06 10:48:18AM

The "enableRAID" command to change an existing active volume into a RAID slice doesn't always work (diskutil sometimes refuses to do this). The scheme outlined above is also a bit risky, since "enableRAID" rewrites low-level format info on the boot disk -- you should really back up first. Here's a safer and surer way to turn your boot disk into a RAID group without down time and without installing OS X on the new disk.

The basic idea is to turn the new disk into an empty RAID slice (this seems to always work) and then copy the boot disk onto it. Boot up into this one-disk RAID group, and then turn the original boot disk into the second RAID slice. This is safe because you've already successfully booted into the copy before you overwrite the original. In more detail:

1) I started by using Disk Utility to erase the new drive I was adding. (Or OS X may offer to do this for you when you first plug the drive in). I named the new drive "BootRAID". I then quit Disk Utility and from a terminal window ran "diskutil enableRAID mirror /Volumes/BootRAID".

2) I then restarted Disk Utility, clicked on the new drive and used the Restore option to copy the boot disk onto "BootRAID". Note that the new drive has two entries in the list of volumes (slice name and RAID group name) and only one of these has the Restore option.

3) When the copy was complete I selected "BootRAID" as my boot disk in System Preferences and rebooted. This reboot was the only downtime.

4) Now I was booted into the one-disk (degraded) RAID group and I again used the graphical Disk Utility and dragged the old boot disk into the RAID
group. This erased the old boot disk and started the mirror "repair".

The repair copied the mirror disk onto the original disk, and a few hours later I had an intact mirrored RAID group as my boot disk.

(I sent a similar comment to afp548 a few months ago).

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safer and surer
Authored by: mrdelurk on Nov 04, '07 04:59:11PM

The task was, get rid of my OSX 10.4.10 dual Mac G5's system drive (it's both a puny 160 Gig and Maxtor - two major strikes) and replace it with a RAID of two 400 Gig Western Digital SATA HDs I freshly bought.

I tried the "clone System to external drive, boot from it, install RAID" approach plink53 suggested, it didn't work. I had the system HD cloned both to a FireWire and an USB external hard disk, neither budged an inch at boot time. Even if they did, Disk Utility wouldn't let me add internal SATA drives to the RAID window, only external FireWire ones.

Next I tried inviscid's "enableRAID, restore to mirror, restore to system HD" approach. It didn't work either. After the enableRAID step, Disk Utility still didn't report any kind of RAID, degraded or not. Even if it did, the 400 Gig internal SATA drive which was duped from the 160 Gig System drive with the Restore command would not boot the computer no matter what I tried.

So these RAID concepts are nice, but the feedback from the trenches is, they don't necessarily work.

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safer and surer
Authored by: Shanghai_David on Jun 08, '08 06:06:01PM
This was very helpful to me and everything worked -- except for the last step when Disk Utility gave an "Unrecognized Filesystem" error and refused to rebuild the new RAID disk.

I finally solved things using Terminal diskutil commands (which worked perfectly) after following the guide by Robin Daugherty I found in (modifying Robin's third Terminal command to include the "member" keyword) so the Terminal commands become:

diskutil list (to find the partition that is going to be added)
diskutil checkRAID (to get the RAID UUID)
diskutil addToRAID member <device name> <raid uuid>

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Enable RAID on the boot disk without a reinstall
Authored by: briank on May 10, '08 06:23:14AM

Mirroring a *data* drive via this method works great. Unfortunately, my 933MHz G4 PowerMac (running 10.3.9) refuses to boot from a mirrored boot drive. No harm done, I'm just going to start anew, probably with a hardware RAID setup. But don't waste your time trying this on a 933MHz G4 boot drive.

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Enable RAID on the boot disk without a reinstall
Authored by: briank on May 10, '08 09:22:28PM
BTW, this hint appears to have been modified from a very similar hint here in case anyone is interested in the original. --Brian

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