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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

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

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  • by Christopher Murphy,

    Christopher Murphy Christopher Murphy Nov 30, 2012 9:50 AM in response to blaqink
    Level 3 (555 points)
    Nov 30, 2012 9:50 AM in response to blaqink

    Auto rebuild applies to a temporarily missing member that's reinserted. i.e. if you pull a member drive and shelve it, replacing it with some other drive (rebuilding it manually), later you can swap the three drives around and a rebuild of the non-synced drive will automatically start. It can do this because of metadata on each of the drives indicating what array it belongs to. Once formatted, this metadata is gone so an autorebuild of that drive won't happen.

     

    http://support.apple.com/kb/HT3305

    http://www.techrepublic.com/blog/mac/how-to-rebuild-raid-sets-properly-in-snow-l eopard/811

  • by blaqink,

    blaqink blaqink Nov 30, 2012 2:25 PM in response to Christopher Murphy
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    Nov 30, 2012 2:25 PM in response to Christopher Murphy

    thanks for the response. i saw those guides however when i go to rebuild the rebuild button is greyed out, that is my main issuse. i replaced the one that says missing with the drive thats called new member and the rebuild option is still not available

    Screen Shot 2012-11-30 at 2.20.00 PM.png

  • by Christopher Murphy,

    Christopher Murphy Christopher Murphy Nov 30, 2012 2:41 PM in response to blaqink
    Level 3 (555 points)
    Nov 30, 2012 2:41 PM in response to blaqink

    The instructions I'm reading say you're supposed to click on the RAID Set, not the RAID Slice as in your screen shot. What happens if you click on the RAID Set, is Rebuild available? If not what happens if you click on the missing RAID Slice, delete it, then either click on New member or RAID Set - is Rebuild available with either of those?

  • by blaqink,

    blaqink blaqink Nov 30, 2012 2:45 PM in response to Christopher Murphy
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    Nov 30, 2012 2:45 PM in response to Christopher Murphy

    even if i click raid set there is no option to rebuild. when i delete the missing RAID slice then it is no longer a raid setup anymore and the one drive that was okay has now just become a seperate drive with no raid slice partition

    Screen Shot 2012-11-30 at 2.42.41 PM.png

    as soon as i deleted the missing RAID slice this list disappeared

  • by Christopher Murphy,Solvedanswer

    Christopher Murphy Christopher Murphy Nov 30, 2012 2:59 PM in response to blaqink
    Level 3 (555 points)
    Nov 30, 2012 2:59 PM in response to blaqink

    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.

  • by blaqink,

    blaqink blaqink Nov 30, 2012 3:03 PM in response to Christopher Murphy
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    Nov 30, 2012 3:03 PM in response to Christopher Murphy

    excellent that solved my question! i had to click the missing drive hit the minus button then the demote button showed up, after demoting the drive it dissapeard and i was able to rebuild with the new drive.
    thanks!

  • by Christopher Murphy,

    Christopher Murphy Christopher Murphy Nov 30, 2012 3:09 PM in response to blaqink
    Level 3 (555 points)
    Nov 30, 2012 3:09 PM in response to blaqink

    Yeah I forgot to mention that I click Missing Device, then the minus button, THEN I had a Demote button. Seriously the RAID part of Disk Utility is one of the most hideous UIs I have ever seen from Apple.

  • by blaqink,

    blaqink blaqink Nov 30, 2012 3:18 PM in response to Christopher Murphy
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    Nov 30, 2012 3:18 PM in response to Christopher Murphy

    agreed! also the rebuild process has been stuck on estimatimated time left in rebuild: calculating..
    does it usually take a long time? there are only a couple of test files on the hard drive.

  • by Christopher Murphy,

    Christopher Murphy Christopher Murphy Nov 30, 2012 3:25 PM in response to blaqink
    Level 3 (555 points)
    Nov 30, 2012 3:25 PM in response to blaqink

    In a virtual machine with a 20GB RAID Set (2 mirrored 20GB virtual disks), it took 5+ minutes. Mirrored arrays duplicate at a block level, so every single block must be copied from one to the other anytime there is a rebuild. With two 3TB drives, I'd expect the rebuild to take a couple of hours. And Disk Utility on 10.6.8 at least, hangs totally during this time, although I can use other apps.

     

    The long rebuild time is why I recommend RAID 10 instead of RAID 0+1; and RAID 1 + linear/concat, instead of linear/concat + RAID 1, when setting up nested RAID levels. Of those four options, only RAID 1 + linear is easily expanded merely by adding two more disks (which themselves need to be the same size, but they can be a different size then the other drives in the original concat).

  • by knutsen,

    knutsen knutsen Jan 5, 2013 9:46 AM in response to Christopher Murphy
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    Jan 5, 2013 9:46 AM in response to Christopher Murphy

    Thank you! First format the replacement drive ("Untitled" will do for a name), then delete the Missing slice, then Demote the RAID Set, then drag in the replacement drive and Rebuild. WHY is this not in the Help?

  • by Highks,

    Highks Highks Oct 19, 2013 2:15 PM in response to blaqink
    Level 1 (0 points)
    Oct 19, 2013 2:15 PM in response to blaqink

    Awesome, this just saved my sanity, thank you!

     

    I was about to go totally insane when I couldn't find the option to add a new drive to the existing RAID mirror and then rebuild the whole thing.

     

    In the Apple help, it just says "go to RAID" "click rebuild" - but this is absolutely not how it works!

     

    Adding the new, empty drive by drag and drop wasn't mentioned anywhere - in addition to that I have never seen a program that has certain functions which can only be accessed by drag and drop.

    Also the hard disk utility doesn't look like drag and drop GUI at all.

     

    It was really easy as soon as I read this thread, so thanks again, this totally saved my day!

  • by Projectorize,

    Projectorize Projectorize Aug 13, 2014 7:01 AM in response to blaqink
    Level 1 (0 points)
    Aug 13, 2014 7:01 AM in response to blaqink

    Goodnes gracious!

     

    When i press - and demote, i get the message saying, it will not affect the data on the raid, but be aware that after demote, you can no longer assemble the raid again.

    What does that mean, that i "just replace a missing disk" but i cannot rebuild it? I hope the engineer behind this never got his last salary...

    So, what do i have to do to get my data back up and running again?

    Im trying to copy from the remaining disk, but after a little while it disconnects automatically with the message "disk was not ejected, please..."

    Has the failing disk something to do with this? Do i need backup of the backup of the backup to recover from a crash?

    Cant get more confused and frustrated than i am know...

  • by Christopher Murphy,

    Christopher Murphy Christopher Murphy Aug 13, 2014 9:18 AM in response to Projectorize
    Level 3 (555 points)
    Aug 13, 2014 9:18 AM in response to Projectorize

    Instead of hijacking a nearly year old thread and ranting, I suggest starting a new thread and explain why you're even clicking on the minus button in the first place. What are you trying to achieve? Have you had a drive failure? Have you replaced the failed drive?

     

    Pressing the minus button breaks the RAID, i.e. it separates the drives, removing them from RAID.

     

    How to rebuild a software RAID mirror

  • by Projectorize,

    Projectorize Projectorize Aug 13, 2014 9:34 AM in response to Christopher Murphy
    Level 1 (0 points)
    Aug 13, 2014 9:34 AM in response to Christopher Murphy

    Sorry, didnt knew i had to start a new thread when another is less then a year old.

     

    I was just following the suggestions in this thread, you were also the one that mentioned the minus button.

     

    Anyway, my concern was the same as the OP.

    One drive has failed in a mirror raid 2, it says missing, replacing it with a new drive doesnt do anything, so how do i rebuild the drive then, when rebuild button is greyed out no matter what disk i choose?

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