And yet another attempt: Command (m for help): n All primary partitions are in use. Adding logical partition 6 First sector (86247424-3907029167, default 86247424): 86507520 Sector 86507520 is already allocated. First sector (1135085568-3907029167, default 1135085568): 1135083520 Value out of range. So entering a bad sector number forces fdisk to recompute the lowest sector, and then it proposes a working value.