Card volume: 11x15x0.7 mm³ = 1.155e-7 m³

4U-Rack volume: 450.85x(4*44.45)x800 = 64.128904e-3 m³

At 100% usable volume ratio that would be 555228 Micro-SD-Cards or 222 Petabyte and cost $55,000,000,000 (assembly and shipping not included).

The storage density of the cards is 2.77e19 bit/m³.

Assuming a saturated gigabit (100 MB/s) connection, uploading your backup would take 70.4 years.