  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 $\mathcal{O}(10^{-10}){\rm Hz}\lesssim f_{\rm
GW}\lesssim\mathcal{O}(10^{-5}){\rm Hz}$, 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.
