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Apple + Tech

Tip: Making Two Hard Drives Appear as One

I conceded defeat.

In December last year I wrote that I was going to stop adding content to iTunes. My aim was to avoid having to buy 2TB hard drives – surely 1TB was enough media!

Well little over four months later I succumbed and bought that 2TB hard drive. In fact I bought 2 of them. The trigger was the failure of one of my 1TB Western Digital external drives. That drive had a 3 year warranty so I took it back to Officeworks. They offered to replace the drive or give me a gift voucher for the purchase price. I’d intended to ask for a replacement, but I’d just seen that the price of a 2TB drive was now less than what I’d paid for the failed 1TB drive. So I took the gift voucher. A few days later I took that voucher into another Officeworks store and bought the 2TB version. I call this the consumer strikes back … yes, it’s not hard to justify our actions sometimes!

Because of my attempts to follow the 3-2-1 backup strategy (3 back ups, 2 different types of media, 1 offsite) the use of a 2TB drive meant that I needed 3 x 2TB drives (or equivalent). Which is why I bought the second 2TB drive. And is why I needed to span two of my other drives into one hard drive so that I had my third backup.

I use the term “span”, but that might not be the right term. When I googled it I came up blank. But I know that Apple Disk Utility does this sort of stuff, so I played around for 5 minutes – seriously, this only took 5 minutes – and I had 2 x 1TB external drives that appeared in the Finder as 1 x 2TB drive. And SuperDuper! is happy to clone to that 1 x 2TB drive. Brilliant!

The correct term is Striped Raid. And wikipedia tells me it’s RAID 0.

And it’s easy.

  1. Open Disk Utility: Applications > Utilities > Disk Utility
  2. Click the RAID tab
  3. Select Striped RAID Set from the RAID Type selector
  4. Name the RAID set
  5. Drag the disks/partitions to be included into the list
  6. Click create.
  7. You’re done!

Striped Raid: easy to set up via Apple Disk Utility

In the diagram above:

  • RED boxes = steps 2 and 3 above
  • GREEN boxes = the 2 slices for my (previously created) RAID set
  • YELLOW box = the combined RAID set. This also appears in the Finder.




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