Unable to rebuild in mirrored RAID after hard drive failure

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

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?

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.

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.

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).

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?

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! 🙂

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... 😠

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

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?

Please post a screen shot.