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Software RAID Question: RAID Slice Missing

post #1 of 4
Thread Starter 
I'm having a RAID issue and was hoping someone could clarify. At work, we're using a Sonnet Tempo SATA E4P to connect two Lacie 8TB RAID drives (4Big models) via ESATA. These two 8TB drives are mirrored via Software RAID.

We had some issues with the power supplies failing due to the person that originally set it up. Essentially, the power supplies were all wrapped up together and stuffed into a hot corner causing them to fail.

Since then, I've ordered new power supplies and placed them in better areas. The RAID finally mounts again, but I have this error in Disk Utilities

I've tried repairing the degraded RAID twice without any progress.. I guess the weird thing is the RAID Slice (E6243AE1-DCA9-4171-AD9B-68169384350B) is missing.. I'm not sure what that is or if it should even be there because we only have two drives connected.

Can i simply remove it from the RAID Set? I'm very concerned about losing data. Once I have this operational again, I can back this thing up and convince them to move over to a Hardware RAID system

post #2 of 4
Apple has a command-line guide for dealing with degraded mirrored RAID here:


If you use the terminal and type diskutil list, does it give you any more information about the missing slice?

Also, what does Disk Utility show when you eject and turn off either of the drives? Does it still show 3 slices as being part of the RAID set?

If so, it seems like what might have happened is one drive went out of sync due to the PSU failing and your repair and rebuild has added an extra drive to the RAID set as Apple's software RAID supports more than 2 drives.

There is a command-line option to remove a spare drive from a mirrored set, which looks like the following:

diskutil appleRAID remove UUID /Volumes/RAIDname

The UUID is the long number in brackets so in your case, removing the missing slice would be done using:

diskutil appleRAID remove E6243AE1-DCA9-4171-AD9B-68169384350B /Volumes/CUBE_02

If at any point it says you don't have permissions, add sudo in front of the command e.g sudo diskutil... and it will ask for your password.

I'm not sure if the delete button in the UI does the same thing but it seems to indicate that it will instead destroy the entire RAID set. The command-line has that option too and says that this will cause the mirrored drives to remain in tact but as separate drives but has some element of risk, although it says that about any RAID operations.

I'd personally use the above command to remove the offending slice from the set.
post #3 of 4
Originally Posted by zarishpk View Post

Your data is still in tact due to one of the mirrors isn't damaged (hence the Degraded state = data's there, but runs slower, and is in danger of data loss). If a disk dies in the functional LaCie box, your data = gone.
can you read from the 8tb cube_02 mirror?
It's in a Degraded state, but is still accessible.

Oh look.. exactly the same answer as someone else posted here:http://forums.macrumors.com/showpost...87&postcount=3

... and written in pretty good English, unlike the rest of your posts.

So when can we expect the sig spam?

Marvin, are you there with your Big Mod Scissors?
post #4 of 4
Originally Posted by piot View Post

Marvin, are you there with your Big Mod Scissors?

Snip, snip . Thanks for pointing it out.
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