Creating a virtual machine clone of the host computing device and handling of virtual machine clone requests via an I/O filter

A computing device, comprising:

• at least one processor;
• and
• a storage medium including instructions that, when executed by the at least one processor, cause the computing device to execute:
• a host operating system on the computing device;
• a hosted hypervisor executing within the host operating system, the hosted hypervisor capable of managing one or more virtual machines, the hosted hypervisor configured to
• receive a request to boot a virtual machine clone of the computing device on the computing device from which the virtual machine clone is cloned;
• in response to the request, synthesize, by the hypervisor, for each local physical disk of the computing device, a virtual disk that is comprised of a master boot record (MBR) of the computing device, a read-only snapshot obtained from a volume snapshot service of the host operating system of the computing device from which the virtual machine is cloned and a delta virtual disk, wherein the synthesized virtual disk is a thinly provisioned virtual machine disk initially of a same logical size as the MBR contained in a first sector of the synthesized virtual disk, and subsequently grows as changes are made to the delta virtual disk over time;
• and
• boot the virtual machine clone of the computing device from the synthesized virtual disk on the computing device from which the virtual machine clone was cloned;
• wherein booting the virtual machine clone includes deploying an input/output (I/O) filter in the hypervisor and attaching the I/O filter to the synthesized virtual disk, the I/O filter configured to intercept disk block requests from a guest operating system (OS) of the virtual machine clone before the disk block requests are passed to a virtual disk of the virtual machine clone, wherein the I/O filter:
• in response to a get disk size request, returns a size of the corresponding local physical disk of the host computing device;
• in response to a read block request, fetches the block from the read-only snapshot if the block is part of a partition of the corresponding local physical disk, otherwise, if the request is for the MBR or for a block that is not part of any partition, it is passed on to the thin-provisioned virtual machine disk;
• and
• in response to a write block request, fails due to the I/O filter providing only read-only access, wherein all write block requests are passed to the delta virtual disk.

A non-transitory computer readable storage medium comprising one or more sequences of instructions, the instructions when executed by one or more processors causing the one or more processors to execute the operations of:

• in a hypervisor running within a host operating system on the host computing device, receiving a request to boot a virtual machine clone of the host computing device on the host computing device from which the virtual machine clone is cloned;
• in response to the request, synthesizing, by the hypervisor, for each local physical disk of the host computing device, a virtual disk that is comprised of a master boot record (MBR) of the host computing device, a read-only snapshot obtained from a volume snapshot service of the host operating system of the host computing device from which the virtual machine is cloned and a delta virtual disk, wherein the synthesized virtual disk is a thinly provisioned virtual machine disk initially of a same logical size as the MBR contained in a first sector of the synthesized virtual disk, and subsequently grows as changes are made to the delta virtual disk over time;
• and
• booting the virtual machine clone of the host computing device from the synthesized virtual disk on the host computing device from which the virtual machine clone was cloned;
• wherein booting the virtual machine clone includes deploying an input/output (I/O) filter in the hypervisor and attaching the I/O filter to the synthesized virtual disk, the I/O filter configured to intercept disk block requests from a guest operating system (OS) of the virtual machine clone before the disk block requests are passed to a virtual disk of the virtual machine clone, wherein the I/O filter:
• in response to a get disk size request, returns a size of the corresponding local physical disk of the host computing device;
• in response to a read block request, fetches the block from the read-only snapshot if the block is part of a partition of the corresponding local physical disk, otherwise, if the request is for the MBR or for a block that is not part of any partition, it is passed on to the thin-provisioned virtual machine disk;
• and
• in response to a write block request, fails due to the I/O filter providing only read-only access, wherein all write block requests are passed to the delta virtual disk.