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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 http://discussions.apple.com/message.jspa?messageID=5782396#5782396 (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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