Turns out AppleRAID is a lot like disksuite (except appleraid seems to drop disks out for no reason a lot of the time, and there’s no UI to tell you that happened).
Turns out you can ‘removefromraid’ one half of a mirror and the detached disk’s appleraid partition gets turned into HFS+ and mounted by the OS (great).
Problems happen when you removefromraid the remaining disk, mac os doesn’t manage to repartition properly (probably because I hadn’t unmounted the raid device).
imac:/Users/chrisl/ 1$ diskutil removefromraid 796AC197-9255-4747-AF1C-A62F05BA3451 B1EC6D40-F0BE-49EE-AAA5-945983DF5A65 Changing filesystem size on disk 'disk2s2'... Attempting to change filesystem size from 499763871744 to 499763888128 bytes The disk has been removed from the RAID
You end up with the partition having its ID left as ‘Apple_RAID_Offline’ and it’s not mountable and first aid refuses to try and fix it:
imac:/Users/chrisl/ 67$ gpt show disk8 start size index contents 0 1 PMBR 1 1 Pri GPT header 2 32 Pri GPT table 34 6 40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B 409640 976101344 2 GPT part - 52414944-5F4F-11AA-AA11-00306543ECAC 976510984 262144 3 GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC 976773128 7 976773135 32 Sec GPT table 976773167 1 Sec GPT header
everything’s in index 2 – 52414944-5F4F-11AA-AA11-00306543ECAC.
http://developer.apple.com/technotes/tn2006/tn2166.html tells me that’s Apple_RAID_Offline and that 48465300-0000-11AA-AA11-00306543ECAC is ‘Apple_HFS’.
Turns out you can delete and re-add the partition though since we still have the start and size:
imac:/Users/chrisl/ 3$ gpt remove -i 2 disk8 disk8s2 removed imac:/Users/chrisl/ 102$ gpt add -b 409640 -s 976101344 -t 48465300-0000-11AA-AA11-00306543ECAC disk8 disk8s2 added
and the OS will immediately mount the partition. This is handy if you formatted the drive you detached first without checking the other drive is okay to be used.
I could give you a hug right now for posting this. Seriously.
You have NO idea how grateful I am for this info.
Saved my bacon today. Thanks!
Thank you so very much!!!
You have saved me lot of work and recovered 600GB of data!!!!
Please add my grateful thanks for this tip. It also bailed me out of the poo. You are a legend !.
You saved me, again. I did the same mistake twice 6 months apart.
Thank you. Thank You.
Hello can I do the same or something similar for drives that failed to mount after I took them out of a LaCie 2big quadra set as mirror raid ?
when I put them back inside the computer asks that I format them …
Data rescue can see the data but when I run it is generate more files and content that I had and it is not usable as such…
These are 3 important final cut project…
Thank you for your help …
Saved my butt today. Thank you, sir.
Have been trying to fix a 2-drive raid that keeps losing a disk. Worked fine until two hours ago, now not, following your info and this (https://forums.macrumors.com/threads/recovering-a-raid-drive-that-wont-mount.799749/) which references the old link to this page, I now have a path forward. Which I will follow after sleeping on it. Things haven’t changed much under the hood between when you posted this to 10.13.6. Wish me luck. And thanks.
Let’s just say that what I learned here allowed me to recover what needed to be recovered. In the process I also learned never to use AppleRAID ever again. Never. Data secureity requires something other than a 2010 iMac managing a mirror RAID on an OWC Firewire drive. I now have a proper FreeNAS appliance and push it all to Backblaze. Now I can sleep at night. But you helped the process along, and for that, I thank you.