The popularization of both virtualization and CDP technologies mean that we can now watch disk accesses of systems from entities which are not controlled by the OS. This is a rich source of information about the system’s inner workings. In this paper, we explore one way of mining the stream of data, to determine if the system had finished booting. Systems which we detect as failing to boot (or taking too long to boot) are flagged for further manual or automatic remediation. By performing this detection out-of-band, we gain a head start on any detection scheme that runs within the OS, and therefore must wait for the boot event to finish. Additionally, our scheme is agnostic to file-system layout and to kernel architecture. We implemented our solution for the x86 architecture under two different virtualization platforms, and tested it on both Windows and Linux virtual machines. Under a variety of workloads and configurations, our detector managed to successfully identify the boo...