Abstract: A system to rebuild a difference virtual hard disk (VHD) for updating an operation system (OS) and a method thereof are provided. After a setting host updates a OS contained in a parent VHD, a service host uses the parent VHD as a base image to build a difference VHD. After the service host writes system setting data into the difference VHD, a virtual machine (VM) executed by the service host loads the updated OS. The updated OS executes the agent after startup so that the agent sets the operating environment according to the setting data. The system and the method need not to update OSes using the same base image respectively, and can achieve the effect of increasing the efficiency of updating the OS using the same base image, and decreasing network traffic when updating the OS.

Abstract: A server, a host and a method for reading the base image through a storage area network (SAN) are provided. A setting host builds a parent virtual hard disk (VHD) in a storage server through an SAN. The parent VHD is used as a base image to build a difference VHD in a local disk by the service host. After a virtual machine (VM) operated on the service host mounts the difference VHD and when the VM executes a target program, the service host reads original data in the parent VHD through the SAN and accesses difference data generated by the target program in the difference VHD in the local disk. The server, the host and the method can configure base image and difference VHD on different devices, and can achieve the effect of increasing access performance and number of supported VMs of the storage server.