RAID 1 - Slice failed - How to rebuild

[victor.espina]

Hi. I have a Mac Mini Server with two 1 TB HD configured in a RAID 1 set called "serverhd". A few weeks ago, one of the slices came with the status "failed" and now the whole set is "degrated".

The SMART status of the failed drive is OK, so I think this is not a case of disk failure. All the details can be found here: https://discussions.apple.com/thread/6787481

My question is: how can I reformat the faulty disk and rebuild the RAID set so both disk go back to normal again?

TIA

Victor Espina

 

[Les Kern]

Since RAID 1 is a simple mirror, just split the disks, then, if you had set AutoRebuild when making them, just reformat the disk and let it rebuild automatically. If you didn't, open disk util, select the RAID and rebuild from there.
Which brings me to a different method that I use. Since RAID 1 really gives no benefit besides a slightly faster read (and unaffected write) speed, I decided to forgo using RAID 1 and rely on other methods to keep a backup, usually Carbon Copy Cloner and Time Machine. Never lost a file when using the method in a robust way, and was tired of failing RAIDS. Just a thought.

 

[victor.espina]

Thanks for your answer. Just be clear:

1. I must boot on the server from an external drive, maybe an USB, with a clean copy of Maverick
2. Run the Disk Utility
3. Remove the faulty disk from the RAID set
4. Erase the faulty disk
5. Add the formatted disk to the RAID set
6. Press the Rebuild button

The benefit I see from the RAID set is that if one disk fails, I can keep working with the other disk with no downtime. A backup approach will always include some mayor downtime while the backup is restored.

Victor Espina

 

[Les Kern]

Thanks for your answer. Just be clear:

1. I must boot on the server from an external drive, maybe an USB, with a clean copy of Maverick
2. Run the Disk Utility
3. Remove the faulty disk from the RAID set
4. Erase the faulty disk
5. Add the formatted disk to the RAID set
6. Press the Rebuild button

The benefit I see from the RAID set is that if one disk fails, I can keep working with the other disk with no downtime. A backup approach will always include some mayor downtime while the backup is restored.

Victor Espina

No need to boot from an external. You can split the RAID live then do the check and rebuild. Of course this assumes you've backed up the data to at least two places to keep it safe. I would suggest using SuperDuper or Carbon Copy Cloner to do a bit for bit rsync backup. I never like to mess with production data without some serious precautions.

 

[sfpete]

Les... you state:

"Since RAID 1 really gives no benefit besides a slightly faster read (and unaffected write) speed, I decided to forgo using RAID 1 and rely on other methods to keep a backup, usually Carbon Copy Cloner and Time Machine. Never lost a file when using the method in a robust way, and was tired of failing RAIDS. Just a thought. "


RAID 1 is not intended to be, nor should it be used as a *backup*. RAID 1 is used for redundancy. In server applications this relates to uptime. 1 drive can fail and the entire server can carry on... hot... with zero downtime.

The suggestions you make with Carbon copy cloner are more relating to backup. If a server with 1 (Boot) drive dies... in the middle of the night... it's down. Sure you can boot from the clone, but that doesn't help when you have countless users accessing.

With that all said, the RAID 1 mirror implementation in software for Mac is pretty bad and does seem to fail from time to time like the OP stated. We used to deploy mirrors like this.. and had similar issues. We've had much better success with deploying SSDs with a clone to an external drive. Yes, it doesn't help with the uptime... but the failure rate on SSDs is quite low.

 

[unplugme71]

With the Mac Mini Server, I used RAID 1. Now with the new models, I don't use RAID anymore.

I bought another Mac, and have it act as the secondary OD, DNS, DHCP server. So I just promote it to a master, build up the broken Mac, and then set it up as the slave. Then I promote it back, and demote the slave.