Most appliance disappointments are sizing failures wearing a hardware costume. The platform performs exactly as specified; it was simply specified against capacity when it should have been specified against recovery.
Two Different Questions
Capacity planning asks whether the data fits. Restore planning asks whether it comes back in time. Only the second one is a recovery objective, and only the second one is tested on the day that matters.
The Inputs That Move It
Data volume, daily change rate, retention length, and restore concurrency drive the requirement. Change rate is the figure most often estimated from memory, and it distorts the outcome more than any other input.
Specifying Properly
A correctly sized data backup appliance is specified against measured change rate and a defined restore-time target rather than against a headline capacity number that says nothing about how fast data moves back.
Headroom for Synthetics
Synthetic full operations consume substantial I/O on the platform. A design without headroom for them will either build recovery points late or slow concurrent restores, and both failures surface under pressure.
Size for the Cycle
Specify against growth across the whole refresh period. A platform that fits precisely on day one has no room for the estate it will actually be protecting two years from now.
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