RAID my disk

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RAID my disk

Dear All,
I want to mirror my old (external hard disk) shared disk with my new WD external hard disk. Any time I try to mirror them I get a message "to create mirror all in formation will be lost from following disks" there is both hard disks my old and new. I dont want to lose my data from my old disk.

Is there any way I mirror my old disk with new one without losing my data from old disk?

Here are the steps I followed
1. Disk Utility
2. RAID
3. dragged and dropped both disks in box in the right hand
note: If I drag and drop on volume the Create button does not activate I have to drag and drop both volumes.
4. Create

After pressing the Create button I get message says the data will be lost from both volumes.

Thanks
Tiger07

Mac OS X (10.3.x)

Posted on Mar 25, 2010 3:10 AM

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Answer 1

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Camelot

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55,305 points

Mar 25, 2010 8:51 AM in response to tiger07

Disk Utility.app will always erase the drives when creating a mirror.

The solution is to use the command line to convert the old drive to a degraded mirror (e.g. a mirror with only one disk), which you can then 'repair' by adding the second disk in (either via the command line or the GUI).

Start off in the terminal by getting a list of all your disk devices via:

diskutil list

This will show each disk along with its device id, such as:

/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID partitionscheme *500.1 GB disk0
1: EFI 209.7 MB disk0s1
2: Apple_HFS My Mac 499.8 GB disk0s2

You'll have one such block for each disk. Once you identify which disk is the 'old' disk that you want to retain the data on you can use diskutil again. For example, if the disk was disk2 you would:

diskutil enableRAID mirror disk2

This will convert disk2 into a degraded RAID mirror volume without destroying its contents. If you run diskutil list again you'll see a new RAID device has been added.

If you're comfortable enough in the command line you can 'repair' the mirror by adding the second drive in:

diskutil addToRAID member disk3 disk4

The above command will add disk3 as a new member of the RAID volume disk4 (which was created as a result of the enableRAID command).

One caveat - the syntax of various diskutil commands has changed over the OS versions - some versions want disk IDs (e.g. 'disk1', 'disk2'), some want slices (e.g. 'disk2s2' as taken from the last column of diskutil list), so don't be too concerned if the commands don't work exactly as I've posted them - I don't completely remember which OS version requires which format, nor know which version you're running.

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Answer 2

tiger07 Author

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Mar 26, 2010 2:48 AM in response to Camelot

Thanks a lot for reply .
When I run command
diskutil enableRAID mirror disk1
I got the following error message
" DiskManagementTool [19802] Error writing RAID partition map"
it moves to the next line and does nothing.

My Mac is Mac OS X Server 10.3.9.

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Answer 3

Mar 26, 2010 7:17 AM in response to tiger07

Well, you could use DuskUtility to copy all the data to a 3rd HD, make the mirrored raid, then use DiskUtility to copy the data back to the raid.

Jeff

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Answer 4

tiger07 Author

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Mar 26, 2010 8:33 AM in response to Jeff Kelleher

That disk is quite big I dont have another disk for backup the old one in external disk.

I rebooted the server and run the enableRAID and it worked. Now I have new disk which is disk4

I run command diskutil addToRAID member disk4 disk3 (disk3 is the new desk) and press enter I get a message "most options require root to the device " on next line I get help commands.

I did su root
I still get the same message.

Now when I do diskutil list I have disk5 instead of disk3.

If I want to use Applications->Utilities->Disk Utility Now I have the disk mirror and status Degragated. When I drug and drop the new disk in the box Rebuilt activates with status New. When I press Rebuilt I get a message " Rebuilding a RAID set takes considerable amount of time. All data on the replacement disk will be lost"

Does it going to delete all my data from old disk?

Thanks
Tiger07

Message was edited by: tiger07

Message was edited by: tiger07

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Answer 5

Camelot

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55,305 points

Mar 26, 2010 9:30 PM in response to tiger07

It's fine to use Disk Utility.app to repair the degraded mirror - it's not clear why the command line option didn't work.

When I press Rebuilt I get a message " Rebuilding a RAID set takes considerable amount of time. All data on the replacement disk will be lost"
Does it going to delete all my data from old disk?

No, it's going to erase any data on the replacement disk - i.e. the one you're adding to the RAID. It won't affect data already on the degraded RAID.

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Answer 6

tiger07 Author

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Mar 29, 2010 6:07 AM in response to Camelot

Thanks a lot for all your support. I rebuild it and now both disks are working fine I tested like plugged out the old disk and left the new plugged in and all data are there. I rebooted the server now when I go to Applications->Utility->Disk Utility and then RAID I can see there are both desk with status Degraded.

My last question.
How I know on which disk i am currently working and after how long the data gets transferred from disk1 to disk2?

Regards
Tiger07

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Answer 7

Camelot

Level 9

55,305 points

Mar 29, 2010 7:48 AM in response to tiger07

Oops. In this setup there is no automatic rebuild of mirror RAID, so if you broke the mirror by disconnecting one of the drives the RAID goes degraded and will stay that way until you repair it. It's probably the main reason why I don't recommend RAID using external drives - they're too easy to break from just a cable coming loose.

You'll need to manually repair the mirror by removing the 'FAILED' drive in the array then re-adding it to the array.

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Answer 8

tiger07 Author

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Mar 29, 2010 8:14 AM in response to Camelot

But both disks are running as normal. When I go Disk Utility there is no Fialed or something like that. Both disks has status Degraded when I click on it nothing happens I can not select the disks on the right box. Rebuild button is grayed out and only Delete Set is activated.

Thanks
Tiger07

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Answer 9

tiger07 Author

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Mar 30, 2010 5:47 AM in response to Camelot

Dear Camelot thanks a lot for replies.

If I press Delete Set is it going to delete my data too, or my data will be save. I scare by Delete set I don't want to lose my data.

Thanks
Tiger07

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Answer 10

Apr 17, 2010 2:02 PM in response to tiger07

Isn’t is possible to do this in Disk Utility without harming any of the data on your source disk?

1) Create a mirrored RAID set with only the source disk in it by dragging *only the source disk* to the right-hand side of the window under the “RAID” tab.
2) Click enable. The result will be an online “Mirrored RAID” with only one disk in it.
3) Next, add your second disk to the raid set and click “Rebuild”

I’m pretty sure this works without harming the data on the initial source disk, but I stand open to correction from the disk utility warnings that pop up at each step.

Oh, and I don’t know if this works in 10.3.9.

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Answer 11

Apr 17, 2010 8:45 PM in response to Ryan Androsoff

Just my $.02...
While it is possible to create a RAID via command line tools without erasing the data, something could go wrong. In other words, there ought to be a backup in the first place. I'm all for using advanced options, but sometimes backing up, blasting, and rebuilding isn't such a bad idea.

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Answer 12

Apr 20, 2010 11:40 AM in response to Jeff Kelleher

Ryan Androsoff wrote:
Isn’t is possible to do this in Disk Utility without harming any of the data on your source disk?

1) Create a mirrored RAID set with only the source disk in it by dragging *only the source disk* to the right-hand side of the window under the “RAID” tab.
2) Click enable. The result will be an online “Mirrored RAID” with only one disk in it.
3) Next, add your second disk to the raid set and click “Rebuild”

I’m pretty sure this works without harming the data on the initial source disk, but I stand open to correction from the disk utility warnings that pop up at each step.

Oh, and I don’t know if this works in 10.3.9.

I can confirm that this works using AppleRaid2 - I had to do it the other day. There’s a great article on AppleRaid2 here: http://www.afp548.com/article.php?story=appleraid2-in-depth

According to the article, you can enable a mirrored RAID from one source disk in 10.3 as well. The article notes that doing this is a relatively risky process and, like Jeff says, having a backup is a good idea.

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