Q: Unable to rebuild in mirrored RAID after hard drive failure

I plan on getting a mirrored raid setup for my backups of all my work that I have done. I am currently testing out how the built in software RAID works in OSX.
I have setup a mirrored RAID with two flash drives and it works fine, i then tried to simulate if one of the disks were to fail by reformatting it, and then i tried to plug it back in to rebuild it, but it does not allow me to do so the rebuild button is greyed out. Could it be because i had the RAID setup as automatically rebuild? If someone could walk me through the process of rebuilding the raid setup that would be great, i would like to figure this out before purchasing the harddrives.

Posted on Nov 28, 2012 8:38 AM

I have this question too

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Christopher Murphy

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When I click on RAID Set or the missing RAID Slice, the Rebuild button turns into a Demote button. When I Demote it, the RAID 1 is intact but has only one disk. Then I drag/drop a replacement disk to the Mirrored RAID Set, and then the Rebuild option is not longer greyed out. When I click it the drive is partitioned, formatted, and rebuilt.

Posted on Nov 30, 2012 2:59 PM

Q: Unable to rebuild in mirrored RAID after hard drive failure

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by Christopher Murphy,

Christopher Murphy Aug 13, 2014 10:08 AM in response to Projectorize
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Aug 13, 2014 10:08 AM in response to Projectorize

Please post a screen shot.
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by Projectorize,

Projectorize Aug 13, 2014 10:38 AM in response to Christopher Murphy
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Aug 13, 2014 10:38 AM in response to Christopher Murphy
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by Projectorize,

Projectorize Aug 13, 2014 10:56 AM in response to Projectorize
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Aug 13, 2014 10:56 AM in response to Projectorize

Disregard the previous screenshot...
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by Projectorize,

Projectorize Aug 13, 2014 11:24 AM in response to Projectorize
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Aug 13, 2014 11:24 AM in response to Projectorize

and the raid keeps disconnecting from the computer all the time, after a while, why, bad disk?
It disappears in finder, but the good disk remains in disk utility.
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by Christopher Murphy,

Christopher Murphy Aug 13, 2014 12:47 PM in response to Projectorize
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Aug 13, 2014 12:47 PM in response to Projectorize

If the translation is correct, one is missing and one is failed and therefore the RAID is offline because a minimum of one working drive is required. If you click on the physical drive rather than volume (the line that ends with the word Media), then click the Info button in the toolbar, scroll down and you can see some SMART information that might be useful in diagnosing the problem.
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by Projectorize,

Projectorize Aug 13, 2014 1:07 PM in response to Christopher Murphy
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Aug 13, 2014 1:07 PM in response to Christopher Murphy

I think youre reading the las screenshot where the system has been ejected, the previous one is connected...
Heres the info shot
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by Christopher Murphy,

Christopher Murphy Aug 13, 2014 1:48 PM in response to Projectorize
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Aug 13, 2014 1:48 PM in response to Projectorize

Terminal:
diskutil ar list
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by Projectorize,

Projectorize Aug 14, 2014 12:23 AM in response to Christopher Murphy
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Aug 14, 2014 12:23 AM in response to Christopher Murphy

??
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by Christopher Murphy,

Christopher Murphy Aug 14, 2014 8:50 AM in response to Projectorize
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Aug 14, 2014 8:50 AM in response to Projectorize

Launch the Terminal application, type that command in, and post the results.
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by Projectorize,

Projectorize Aug 14, 2014 9:02 AM in response to Christopher Murphy
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Aug 14, 2014 9:02 AM in response to Christopher Murphy

Before auto eject

After
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by Christopher Murphy,

Christopher Murphy Aug 14, 2014 10:15 AM in response to Projectorize
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Aug 14, 2014 10:15 AM in response to Projectorize

There should be something in Console > system.log that indicates why that RAID slice is going from Online to Failed.

The Apple software raid will be less tolerant of read or write errors than the drive manufacturer, so it's possible for the drive to be "verified" per the drive's SMART self-diagnosis but for it to produce sufficient errors that the software raid will not deal with it. Normally with a 2nd drive as mirror, the RAID continues to operate but there simply isn't anything to be done when both drives have problems.
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by Projectorize,

Projectorize Aug 14, 2014 1:39 PM in response to Christopher Murphy
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Aug 14, 2014 1:39 PM in response to Christopher Murphy

So basically there no such thing as a safe backup then, unless you spread it over a bunch of independent disks?
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by ninephive,

ninephive Mar 23, 2015 6:14 PM in response to Christopher Murphy
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Mar 23, 2015 6:14 PM in response to Christopher Murphy

This method worked for me as well...rebuilding now.
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