I am having serious doubts that the Dell R815's will be profitable in the long term.
u/tevador put together "The profitability of RandomX" calculations for RandomX Hash Rate for profitability of a given rig:
https://www.reddit.com/r/MoneroMining/comments/dxp2h9/the_profitability_of_randomxFirstly, for those who are not aware, the profitability break-even network hashrate H (i.e. the network hashrate at which your electricity costs are equal to your mining rewards) is given (approximately) by the following equation:
H = 30000 * h * R * X / (p * e)
h ... the hashrate at which you are mining [H/s]
R ... the current Monero block reward [XMR]
X ... the current Monero exchange rate [USD/XMR]
p ... the power consumption of your mining device [W]
e ... the price you pay for electricity [USD/kWh]
For example, my Ryzen 1700 mining machine has a break-even point of 30000 * 4250 * 2.1 * 62 / (70 * 0.18) = 1.3 GH/s (assuming a block reward of 2.1 XMR and 62 USD/XMR).
Three of the variables (h, p, e) are specific to your mining setup, the block reward R is more or less predictable and the price of XMR X is unpredictable.
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Using today's price of $51.92 XMR
https://bitinfocharts.com/monero This is what I have measured for four Dell R815 Servers on one PDU.Two with quad 6348 and two with quad 6378 Opterons.
43890 H/s for RandomX
2880 watts (12 Amps * 240 VAC) avg of 720 watts per server measured at the panel.9.0c per KWH
30000 * 43890 * 2.1 * 51.92 / (2880 * 0.090) = 553.8 MH/s
So if the hash rate for RandomX goes to the 1.3 GH/s that is estimated when it settles after the fork these Dell R815's will again be turned off.
I would then only be mining on my various Dell T5600/T7600 Workstations.
I would also look into an electric plan where electricity is free for nights or weekends to mine on the Dell R815's.
Or I would just resell the Dell R815's for a slight profit as most of them only cost me around $250 each.