Adding software RAID to installed system

[Andrew Oliver]

On Feb 6, 2007, at 7:39 AM, Fabian Peters wrote:

> Hi folks,
>
> Has anybody successfully created a RAID1 without erasing the  
> existing boot disk (possibly even w/o rebooting?) on OS X Server  
> 10.4? Apple's "Getting Started" guide states it's ok:
>
> "If the target disk has a single partition and the second physical  
> drive has a single partition and no data, you can set up RAID  
> mirroring after installation."
>
> Which I figure is what I'd like to do but I feel the wording is a  
> bit vague. Of course in any case the usual caveats to back up  
> beforehand do apply...
>
> Thanks for your insights

It is possible to do. You may need to reboot, and you can't do it  
through the GUI.

Assuming your two drives are disk0 and disk1 (use diskutil to verify),  
and disk0 is your current boot drive

1) diskutil enableRAID mirror disk0
This will create a degraded mirror RAID, disk2, consisting of the boot  
drive (disk0) and nothing else.

2) diskutil repairMirror disk2 disk1
This adds disk1 to the existing RAID disk2

3) Wait (use diskutil checkRAID to check progress)

I've done this many times, and it's worked most of the time.  
Sometimes, though, the repairMirror fails. That's usually been fixed  
by booting from DVD and running repairMirror again - in other words  
there's a higher success rate when you do this on a non-live drive,  
but I haven't worked out the exact conditions that cause it to fail.

Andrew
:)