Breaking apart a RAID 1?

December 2, 2006 7:30 AM

Is there any way to "break" a mirrored disk set in Mac OS X (that was created with Disk Utility) back into two separate -- but identical -- drives?

I had bought two 500GB drives to use as a RAID 1 (purely for hardware redundancy) with the idea that if I became desperate for disk space I could break them into independent volumes again.

I assumed it was easy since that's essentially the protection the RAID 1 provides -- one drive goes out, and the other still has all the data. However, I have not seen any examples or steps describing how this would be done. Can it be done?

posted by teradome to computers & internet (3 answers total)

Assuming you're running Mac OS X 10.4, and you have a backup of your data, the following example shows how to remove a drive from the RAID array:

$ sudo -s
# diskutil checkRAID

RAID SETS
---------

Name: DataMirror
Unique ID: 2CFEC74D-5C0C-49CB-940E-6099AE3C2B97
Type: Mirror
Status: Online
Device Node: disk4
Apple RAID Version: 2
----------------------------------------------------------------------
# Device Node UUID Status
----------------------------------------------------------------------
0 disk1s3 EF3F0D87-0E9A-4ED4-BB2B-F2A7EBFD0306 Online
1 disk3s3 B1EC4F22-9C0D-4CDB-90FE-D49347195834 Online
----------------------------------------------------------------------

# diskutil removeFromRAID disk3s3 disk4

You might also repeat this for the first disk and then do diskutil destroyRAID to destroy the RAID array.

Make sure you have backups.
posted by Blazecock Pileon at 7:45 AM on December 2, 2006

You can also do this with the Disk Utility application (in Mac OS X 10.4 deleting a mirrored RAID set leaves a copy of the files on each disk). Here is how you do it:

1. Back up up any important files.
2. In Disk Utility, select one of the disks in the mirrored RAID set that you want to separate and click RAID.
3. Select the mirrored RAID set, then click Delete.

You can also use the Disk Utility application to remove disks from mirrored RAID sets, but I don't know if that leaves the data on the "removed" disk intact.
posted by RichardP at 7:56 AM on December 2, 2006

Since you have to back up anyway (you'd be nuts to experiment with this without backing up), just copy the data to a single drive and reformat the entire original RAID into two drives. You can buy 500GB bare drives for less than $250.
posted by spitbull at 12:56 PM on December 2, 2006