Replace a failed disk in a Disk Utility RAID 1

Question

I have LaCie 2big thunderbolt 2-disk device configured as a RAID1 from Disk Utility. One of the drives appears as "failed", so I unmounted the raid, replaced the drive and plugged it all back in.

Now Disk utility reports that one of the slices is missing from the RAID, and it shows my new disk separately on the list to the left.

The "slices", including the missing one, have a lock icon in front of them, and even after dragging my new disk to the list I can't rebuild the raid.

How do I rebuild the raid?

Answer 1

I was unable to find how to rebuild the RAID from disk utility after a couple of hours of research. However, I managed to do it from the command line.

sudo diskutil list  // to get a list of disks. Note the disk number of your new disk (e.g. disk4)
sudo diskutil appleraid list // note the uuid of the raid in question
sudo diskutil appleraid add member disk4 UUID-OF-YOUR-RAID

It will then kick you back to disk utility and start rebuilding the raid :)

Also, if the failed disk remains on the list, you can remove it:

diskutil appleraid remove UUID-OF-FAILED-DISK UUID-OF-RAID

Answer 2

After plugged it all back in.

Disk utility reports that one of the slices is missing from the RAID, and it shows new disk separately on the list to the left.

You need to delete the missing disk from the right side screen and then click demote.

From the left side, drag and drop the new disk into the right then click on the new media and click rebuild.

Answer 3

You may not actually have a failed drive. If you had a power failure and you don't have all the external drives plugged into the UPS, external drives will be out of sync.

I have two 4 TB drives in my Mac Pro that are mirrored to a pair in external eSata enclosures. Power went off, and I discovered that I had plugged into the 'filtered, but not UPS' plugins on the UPS.

Rebuilding a 4 TB drive takes time -- I have both rebuilds going right now, and it looks like it will be about 12 hours to do them all.