You can add an external bus powered Thunderbolt or USB3 drive easily, and simply velcro it to the back of the stand. The photo shows a Seagate 4TB RAID-0 hard disk, but any size disk or SSD can be used. I can't hear the 2.5" drives in mine, and I set them to power down when not actually being used.
The 4TB is configured as 1TB for bootable clone backup of the internal 1TB SSD, and 3TB additional library storage. It all is backed up over the network to a MacMini Server with external RAID5 drives (backup for all the household computers).
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