From Halopedia, the Halo wiki
During the Forerunner-Flood war, a Forerunner naval group engaged a Flood irregular naval group of 149 non-military vessels over DM-3-1123 b, destroying the contaminated vessels. But the Flood's sole intention was to infest the planet, and within 32 hours, they had overrun local Forerunner ground forces, and only 0.0006% of the planetary population was evacuated (about 1,361,466 individuals out of 226.911 billion). The Forerunner local fleet—upon an 83% consensus—launched a "blanket orbital bombardment" on DM-3-1123 b, destroying the Flood infestation but rendering the planet uninhabitable, following the evacuation of unmolested population centers.
List of appearances