Hypervisor-assisted migration or cloning of eager-zeroed virtual disks

A non-transitory computer-readable medium comprising instruction executable in a computer system, wherein the instructions when executed in the computer system cause the computer system to carry out a method of migrating or cloning a virtual disk stored in a first storage device, wherein the virtual disk was initialized during creation thereof by writing zeroes into all blocks of the virtual disk, said method comprising:

• accessing a data structure that tracks for each block of the virtual disk whether or not the block has been written to successfully since initialization of the virtual disk;
• for each of a plurality of unique sets of blocks, determining using the data structure whether or not any of the blocks in the unique set has been written to since the initialization of the virtual disk;
• and
• for each unique set determined to have at least one block that has been written to since the initialization of the virtual disk, issuing a copy command to make a copy of all blocks in the unique set in a second storage device.

A computer system connected via a network to first and second storage devices, said computer system comprising a processor and system memory, wherein the processor is programmed to execute the steps of migrating or cloning a virtual disk stored in the first storage device and initialized during creation thereof by writing zeroes into all blocks of the virtual disk, wherein the steps executed by the processor comprise:

• accessing a data structure that is stored in the system memory and tracks for each block of the virtual disk whether or not the block has been written to successfully since initialization of the virtual disk;
• for each of a plurality of unique sets of blocks, determining using the data structure whether or not any of the blocks in the unique set has been written to since the initialization of the virtual disk;
• and
• for each unique set determined to have at least one block that has been written to since the initialization of the virtual disk, issuing a copy command to make a copy of all blocks in the unique set in the second storage device.