apple raid missing disk

An Apple concatenated disk set means the disks are accreted together, without any data redundancy, and without any of the performance benefits of RAID 0 when that's used with traditional hard disks.

(RAID 0 means disk striping means similar-sized hunks of the data are scattered across all of the disks with no redundancy. Neither of these approaches are particularly recoverable on hardware failures, unfortunately. RAID 1, RAID 5, RAID 6 and RAID 10 all replicate the data, and will usually permit data recovery after a disk failure.)

With concatenated disks, if there's no backup and if there's no Time Machine, and if powering down the whole configuration and re-seating the failed drive into the bay and powering it all up and trying again doesn't allow access, then you're headed toward acquiring a tool such as DiskWarrior or analogous, or consider contacting a data recovery firm directly to see what they offer and whether they can read and rebuild from the array.

Recovery services will generally require a fee paid, irrespective of whether they're able to recover any data.

Do not apply those Terminal commands, they are not appropriate for your situation. There is no copy of that data. Rebuild commands can only do something for MIRRORED RAID, where there is a complete duplicate copy on the other drive that is still working and Mounted.

Some users have reported success with Data Rescue from Prosoft, which has a free trial period (where you can evaluate what it might do for you before you purchase it.) Data Rescue requires a different drive to save the rescued files, but may be able to reach onto an unmountable drive and grab some files.

Grant Bennet-Alder wrote:

panic moves you could try now, before giving up and doing what MrHoffman says, include:

selecting that wandering drive and running repair disk on it. Repeat until it comes clean or gets hopelessly stuck. If it comes clean, use the "mount" button is disk Utility to mount it, then see if the RAID will accept it back, or what status it gets.

I'm hesitant to recommend sending a whole lot of I/O at a sketchy or failing hard disk drive, as I'd rather (try to) leave the last few "gasps" for the recovery service to try to use during data recovery, rather than finishing off whatever might be failing within the drive with what may be a futile effort to repair it. If it reads at all and if I were inclined to send a fair amount of I/O at a hard disk, I'd tend to try to do a dd-style disk image first, to try to capture whatever data was still readable, while it was still readable. Hard disks don't always degrade evenly or even gracefully, though once they start going visibly weird they're usually pretty far toward gone.

Excellent point, MrHoffman!

My direct "school of hard knocks" experience with Apple RAID is only with Mirrored RAID. I had an instance where one disk dropped out, and it appeared that at the first sign of a Bad Block, it broke the RAID and the errant drive wandered off. I repaired that Bad Block problem once, rebuilt the mirrored RAID from the good drive, and went on with it.

So the on topic part of my story is:

that at the first sign of trouble, the RAID seems to split (at least that is what the mirrored RAID did.) There may still be enough life in it to copy most stuff off.

... back to my "story" and what else I learned:

Then that same RAID drive developed another bad block shortly thereafter. I was not happy about it breaking my RAID again, but while stewing about it I realized that was EXACTLY the behavior I wanted. If the drive had the slightest problem, it was no longer good enough to hold my precious data, and needed to be replaced with a drive that worked absolutely perfectly.

Your suggestions that backups are still needed, even with Mirroring, rings true here.

leocostadj wrote:

Will it work? When you insert the hard disk again will it format this drive? Can you ride the raid?

As Grant Bennet-Alder indicates... Those appleraid commands are not associated with the concatenated volumes in use here. Those commands will not have the desired result here.

I'd further be cautious around whether using appleraid commands might have the side-effect of overwriting some of the existing data still available, too.

FWIW, there's no such thing as a flawless hard disk drive, immediate and newly-deployed failures are common, some number of drives will age out and fail over the average lifetime of the devices, and failures secondary to power glitches are common and whether due to surge or brownout or a generic blown capacitor, and hard disk drives from the same production batch can share the same sorts of design or firmware or specific-batches-of-parts-related flaws...

For hardware RAID, RAID-1 or RAID-6 or RAID-10 or equivalent are preferred.

I prefer to avoid RAID-1, RAID-5 and concatenated.

Whatever is in use, with backups. With off-site backups, if the data is sufficiently valuable.

Stuff always and still will fail, backups will sometimes be unreadable, unfortunately.

Murphy was an optimist.

If you believe the drive is not "near death", there were several suggestions early on in this thread that were possibly appropriate, but were discouraged, because they could push a shaky drive over the edge.

You might want to revisit some of those suggestions in light of what you now believe is happening to the drive.

panic moves you could try now, before giving up and doing what MrHoffman says, include:

selecting that wandering drive and running repair disk on it. Repeat until it comes clean or gets hopelessly stuck. If it comes clean, use the "mount" button is disk Utility to mount it, then see if the RAID will accept it back, or what status it gets.