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I have a MacBook with an SSD, so space is limited.

I've been using a single external drive to store my overflow, but would feel a lot more comfortable if it was on a RAID 1. So, I've bought an 2 bay USB 3 drive case, and an additional hard disk (same exact disk). What I want to do is create a RAID without having to the move the data on the external disk to a new temporary home, if at all possible.

I have:

Disk 1 - contains files.

Disk 2 - empty.

What I would like to be able to do, is create a new RAID 1, with Disk 2 as the only member. It will therefore show that its in a degraded state.

Copy all my data from Disk 1 onto Disk 2 (which is RAIDed). Reformat Disk 1, add it to the Enclosure, and make it a member of the RAID, and have the OS silently replicate the data from Disk 2 to Disk 1, so that it becomes a mirrored set.

Is this possible?

Or do I need to find a 3rd disk to use as a holding area for all of this?

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  • A RAID1/5/6 is no backup device if the data on the drive is unique! A RAID1 is a safety net for one failing drive but not for files & folder accidentally deleted or accidentally formatted drives (i.e. user errors), apps running wild etc. – klanomath Oct 4 '17 at 15:20
  • I understand what RAID is and isn't. But I would like the data on my external drive to be able to survive a drive crash, thanks – Lucas Krupinski Oct 4 '17 at 15:53
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The short answer is no. In any case you should place your data on a third drive, make your raid on drives 1 & 2, then copy data from drive 3 back to the new raid (drives 1&2).

Please note that even raids can (and will) fail too and you should keep a backup of the raid.

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  • I understand what RAID is and isn't (in regards to backup), and do backup to the cloud. But it so happens that I often need access to some files more regularly than what the cloud allows for, hence external storage. – Lucas Krupinski Oct 4 '17 at 15:54

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