Confused about mirr...
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Confused about mirror with an external drive

Active Member Customer


I plan to create a three-disk mirror of some important data. Two of the mirrored drives (10TB each) will be in an OWC RAID enclosure, and the third mirror drive in an external USB3 pluggable container. The mirror volume will contain three partitions, one of which will be a copy of the boot drive, but will not be functioning as a live boot drive (if that makes sense.)

My question - I have read what appears to be confusing advice about how to periodically remove the third (external) drive from the mirror to take it off site (and how to add it back, when re-synching periodically.)

I believe I saw one suggestion of "just turn it off at a quiet moment" (scary?) Another suggestion was "just dismount it", and a third suggestion was "split it off as a read-only secondary drive".

I probably am just confused, but you could clarify the safest way to periodically synchronize the external drive?

Thanks in advance.


Topic starter Posted : 11/11/2019 12:52 am
Member Admin

There are many ways to do this. USB is pretty hot swappable, so you can just remove the disk. Best practice is unmount the volumes, wait 30 seconds or so, then unplug the disk.

However, in your case, you are doing something different. Apple no longer supports bootable RAID volumes. So what you could do is mirror two volume, then use an app like Carbon Copy cloner to make a clone of your boot volume on a schedule. You cannot use it in a mirror.

Posted : 11/11/2019 7:39 pm