We study an inevitable cosmological consequence in PeV scale SUSY-breaking scenarios. We focus on the SUSY-breaking scale corresponding to the gravitino mass $m_{3/2}=100{rm eV}-1{rm keV}$. We argue that the presence of an early matter-dominated era and the resulting entropy production are requisite for the Universe with this gravitino mass. We infer the model-independent minimum amount of the entropy production $Delta$ by requiring that the number of dwarf satellite galaxies $N_{rm sat}$ in the Milky Way exceed the currently observed value, i.e. $N_{rm sat}gtrsim63$. This entropy production is inevitably imprinted on the primordial gravitational waves (pGWs) produced during the inflationary era. We study how the information on the value of $Delta$ and the time of entropy production are encoded in the pGW spectrum $Omega_{rm GW}$. If the future GW surveys observe a suppression feature in the pGW spectrum for the frequency range $mathcal{O}(10^{-10}){rm Hz}lesssim f_{rm GW}lesssimmathcal{O}(10^{-5}){rm Hz}$, it works as a smoking gun for PeV SUSY-breaking scenarios. Even if they do not, our study can be used to rule out all such scenarios.
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