Methods and apparatus are provided for reducing computer system boot up times in systems with composite HDD-SSD storage devices. Booting a computer system having a composite storage device that includes a magnetic storage device (HDD) and a solid state storage device (SSD) includes identifying boot data read from the magnetic storage device during an initial boot process, pinning the boot data to the solid state storage device, wherein pinning causes the boot data to be retained on the solid state storage device during movement of infrequently-used data from the solid state storage device to the magnetic storage device, and reading, by the computer system, the boot data from the solid state storage device during a subsequent boot process. Booting can also include moving infrequently accessed data from the solid state storage device to the magnetic storage device, and the boot data on the solid state storage device.