Creating Mirrored RAID on Startup Disk

Posted:
in macOS edited January 2014
I have a Mac Pro that I want to create a mirrored RAID set in.

I have a 1TB Hard Drive that is the main system drive.

I just added a 2nd 1TB Hard Drive that I wanted to use along with this first hard drive to create a mirrored RAID set.

I used the following document to help with the process:

http://docs.info.apple.com/article.h...sa772e2fc.html



I have opened up Disk Utility and think I may know how to do this but a few things concern me.

First, it states that it will erase the contents of the drives it's using to mirror. I had the idea it would simply duplicate the data onto the other drive. Is it true that it will delete the data on the current drive?



Also, it states that you can't create a RAID with the startup disk. Is that true? I currently have a RAID in this system using the disks in bays 3 and 4. I purchased two 1TB disks and created a SERVER DRIVE raid and this drive is shared with all computers on the network as a data drive. I had no issues setting it up but of course both drives were empty when I created this RAID and also these are not the system/startup drives.



Is there a way I can create a RAID with the main Macintosh HD system/startup disk and also do it without erasing the data from the main drive?



Thank you for your help.

Comments

  • Reply 1 of 3
    Quote:
    Originally Posted by markw10 View Post


    I have a Mac Pro that I want to create a mirrored RAID set in.

    I have a 1TB Hard Drive that is the main system drive.

    I just added a 2nd 1TB Hard Drive that I wanted to use along with this first hard drive to create a mirrored RAID set.

    I used the following document to help with the process:

    http://docs.info.apple.com/article.h...sa772e2fc.html



    I have opened up Disk Utility and think I may know how to do this but a few things concern me.

    First, it states that it will erase the contents of the drives it's using to mirror. I had the idea it would simply duplicate the data onto the other drive. Is it true that it will delete the data on the current drive?



    Also, it states that you can't create a RAID with the startup disk. Is that true? I currently have a RAID in this system using the disks in bays 3 and 4. I purchased two 1TB disks and created a SERVER DRIVE raid and this drive is shared with all computers on the network as a data drive. I had no issues setting it up but of course both drives were empty when I created this RAID and also these are not the system/startup drives.



    Is there a way I can create a RAID with the main Macintosh HD system/startup disk and also do it without erasing the data from the main drive?



    Thank you for your help.



    By the time it took to write this message and wait for a response, you could have cloned the startup disk, created your RAID, and restored from the backup.



    Not sure why you need the startup disk to be a RAID, though. I would suggest using the RAID for data and using an SSD exclusively for the System. That way you don't have to worry about backing up the startup disk at all. If it dies, you just reinstall the system without losing any data, which would be stored on the RAID drives.
  • Reply 2 of 3
    MarvinMarvin Posts: 14,200moderator
    Quote:
    Originally Posted by markw10 View Post


    I have opened up Disk Utility and think I may know how to do this but a few things concern me.

    First, it states that it will erase the contents of the drives it's using to mirror. I had the idea it would simply duplicate the data onto the other drive. Is it true that it will delete the data on the current drive?



    If this is a continuation of this thread:



    http://forums.appleinsider.com/showthread.php?t=115876



    you don't recreate the RAID. You'd use the repair command to rebuild the existing RAID:



    sudo diskutil repairMirror MIRRORNODE NEWDISKNODE



    where the last two values are your drive ids. If you are starting fresh and have a working install on the 1TB drive, building a RAID will erase it. You need to clone to an external, format the internal as RAID and clone back onto the RAID.



    Quote:
    Originally Posted by markw10 View Post


    Also, it states that you can't create a RAID with the startup disk. Is that true?



    You can but not while the system being turned into RAID is running. You'd boot from the external clone or system disk to create the RAID.



    Is there a particular reason for using RAID? Even for local sharing, it seems like overkill unless you have critical files that change significantly during the day. Software RAID can slow things down a bit as the CPU has to keep everything in sync.



    If you are just worried about critical files, a periodic backup system should do the job and this way, if you accidentally delete a file during the day, you are more likely to get it back from the latest backup. RAID1 replicates that deletion immediately.
  • Reply 3 of 3
    I definitely see what you mean. The more I'm looking at it instead of going the RAID route I'm considering Time Machine. I have used that successfully on other systems and it would back up hourly and if I delete a file it won't replicate onto another hard drive. I am sure Time Machine slows down the system some but I think it may be a better option for me to use than RAID. We also have an offsite backup which is done weekly.
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