How remove a raid?

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Level 1

8 points

How remove a raid?

A while back I had idea to streamline my video archiving and add redundancy. Previously had them copied to an external drive no backup which I was running out of space. So I decided buy 2 10tb internal drives and mirror raid them using Mac built in raid ability.

After following instructions using the terminal to create the raid (which seemed to work), I discovered months later even though both drives were part of the raid they were not mirroring. I never received any warning message. I then decided it would better to use a software program to manually sync the drives every few weeks after complete projects were archived.

I proceeded to manually copy the files from one drive to another. Then I pulled the one drive that wasn't mirroring so I wouldn't wipe out both drives and lose all my data when attempting to break the raid. I followed instructions found online, I used the terminal to issue a remove raid command but it wouldn't saying the volume was mounted or something. So then I went into the Hard drive utility and formatting the drive. But despite doing this it still showed up as raid.

So my question is simple how to remove a raid? Do I need to format the drive in a windows machine? Where is it stored that identifies the drive is a raid. I can post screen captures if it would be helpful.

Btw, this is a Mac Pro 2009 running Yosemite.

Mac Pro, macOS 10.13

Posted on Sep 22, 2020 11:54 AM

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Answer 1

Sep 22, 2020 12:35 PM in response to Jetsmac

RAID-ness is recorded in additional partitions on the drive. In order to make the drive NOT a RAID you must completely erase the drive. NB>> you must select the ENTIRE the drive by its immutable Hardware-name, not by user-created names like Macintosh HD name or drive3s1 designation.

High Sierra and later make this far more difficult than necessary by obfuscating the device-name. There is a tiny "View" drop-down in the upper left of Disk Utility that must be set to "Show all devices". Then you will get a screen like this one, where immutable Hardware-names are shown and can be selected.

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Answer 2

Jetsmac Author

Level 1

8 points

Sep 22, 2020 5:40 PM in response to Grant Bennet-Alder

Thanks I think I'll have to take each drive erase them on another system. The hard drive utility doesn't seem to be able restore them back to their original state and Terminal won't alter the drives when given their hardware name.

You can see in screen capture they are showing up as 3 drives when there are only 2.

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Answer 3

Sep 22, 2020 5:57 PM in response to Jetsmac

What is selected in your screen shot shows as a logical partition. You need to erase the ENTIRE Physical device, by its immutable hardware-name. This display is only showing the device-name for that Samsung drive.

I remember that there was a brief period when RAID was omitted from the Disk Utility interface, but I thought you could select devices and erase them regardless.

Are there any menu options that allow you to show all devices?

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Answer 4

HWTech

Level 9

61,406 points

Sep 24, 2020 7:57 PM in response to Jetsmac

I just use the Terminal command line to write zeroes to the beginning of the drive to destroy the partition table and section identifying the drive as part of a RAID.

From your screenshot it appears the drive identifiers for your physical hard drives are "disk1" and "disk3" (at least for this boot when you took the screenshots -- the drive identifiers may be different next time). First thing is to unmount all volumes from those physical drives:

diskutil  unmount  disk1  disk3

If this doesn't allow you to unmount the volumes, then you may first need to unmount "disk5" before unmounting "disk1" & "disk3".

Once all partitions/volumes are unmounted you can zero out the beginning of the drives like this:

sudo  dd  if=/dev/zero  of=/dev/disk1  bs=100m  count=10

sudo  dd  if=/dev/zero  of=/dev/disk3  bs=100m  count=10

You need to confirm the drive identifiers for the physical drives before issues these commands or you may end up erasing something important. Each time you boot the Mac the drive identifiers for those drives may be different.

Once the partition tables are wiped out you can use Disk Utility to erase the drives normally.

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Answer 5

Jetsmac Author

Level 1

8 points

Sep 28, 2020 12:52 PM in response to HWTech

Thanks everyone for your help. I tried the commands you shared and others I looked up. While I was able to unmount the drives and format them, I wasn't able to remove the raid. I ended up using it Western Digital Lifeguard utility on my PC to format the drives, which successfully removed the raid! I'm currently running an extended test that takes 12hrs to insure there is nothing wrong with the drives before putting back into use without the Raid. My guess is that the built in raid of the Mac isn't good. Lesson learned.

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Answer 6

Sep 28, 2020 5:58 PM in response to Jetsmac

My guess is that MacOs was late to implement support in Disk Utility for manipulating RAIDs (they had to re-write Disk Utility in preparation for the introduction of APFS) in exactly the version you have been using, making this job near-impossible.

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Answer 7

Jetsmac Author

Level 1

8 points

Sep 29, 2020 7:55 PM in response to Grant Bennet-Alder

I'm lucky I didn't lose data. Half a year ago after I created the raid someone here warned me it was buggy. Not that I didn't believe him, I didn't know how to undo it and didn't have the time to deal with it. If I ever use one again I would only use a hardware raid. I finished the extended hard drive test, holy crap 16hrs for a 10tb drive.

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Answer 8

HWTech

Level 9

61,406 points

Oct 1, 2020 8:12 PM in response to Jetsmac

Hardware RAID has downsides too. If the hardware card/box goes bad, then you lose all your data unless you can replace the card/box with an identical model plus they usually have restrictions on which drives may be compatible. You also need to use NAS rated drives or Enterprise rated drives in order to have the TLER option on the drive, otherwise the RAID will break.

There are good software RAID based options using Linux. Apple just does not care about RAID.

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