Not possible, write bandwidth of tape is not very high. My guess is they have a cabinet / 42U worth of HDD arrays, by the numbers they need ~ 176Gbps write ban

Not possible, write bandwidth of tape is not very high. My guess is they have a cabinet / 42U worth of HDD arrays, by the numbers they need ~ 176Gbps write bandwidth which is totally possible even in half a cabinet. 400TB worth of SSDs @ 176Gbps write bandwidth is also very possible, would be ~ 4U expect but extremely expensive.