The Internals
Dying to know how a metadata-based storage pool could be so resilient as to survive my crazy (and borderline unrealistic) casualty scenarios, I decided to crack the DroboPro open.  There had to be a secret weapon in there somewhere, and I was going to find it.  Along the way I learned much more about the Drobo than I was expecting to.  Photos of the teardown appear after the following video of me doing a teardown on our This Week in Computer Hardware show, recorded weekly via TWIT Live, with Leo Laporte.



The Case

The case is a simple yet elegant design.  A single sheet of rolled steel ‘wraps around’ the unit, extending forward far enough to surround the magnetic front cover, keeping it in place.  This cover slides off, revealing a rubberized gasket at the front of the unit.  This gasket ensures all suction air is drawn through the front ventilation holes between the drives, resulting in equal cooling to all disks.

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This gasket sits between the front bezel and the metal enclosure to ensure all airflow passes between the drives.

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With the cover removed there is not much to see.  There is the drive cage and what appears to be a cover over the rear half of the unit.  Removing the ‘cover’ revealed it is actually the base of the Drobo’s internal power supply.  The placement is smart in that heat is dissipated by conduction to the large mounting plate and by convection via the stream of air exiting the drive cage.  With the power supply removed I could then see the dual cooling fans and mainboard.

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The Power Supply is built-in.  No bulky power bricks here.

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The mainboard is revealed, along with a pair of 80mm variable speed fans.

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A backplane behind the drive cage handles all of the connections.

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Each of two Marvell 88SX7042-BDU1 SATA controllers handle 4 of the 8 channels.

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(from left) A Marvell 88E1121R-TFE1 GbE interface, the CPU (a dual core Marvell ARM running VxWorks), and on-board SDRAM.

And finally, buried in the back corner is the secret to the DroboPro’s power failure resiliency.  This 7.5 Ah battery pack keeps any in-use metadata preserved for unexpected power failures for a rated 72 hours (rated by Drobo).  Considering the beefy specs of their battery choice, I suspect they were very conservative on that particular spec.

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This battery is beefier than any RAID add-on unit I’ve seen.
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