Abstract:
A method and a system of making a virtual machine space efficient are disclosed. The virtual machine includes a virtual disk. The method includes creating a temporary virtual disk and adding the temporary virtual disk to the virtual machine. The temporary virtual disk works in conjunction with the virtual disk. The virtual machine is configured to store temporary files in the temporary virtual disk rather than the virtual disk.

Description:
BACKGROUND 
     In virtualized systems, virtual machines run in virtualization softwares such as a hypervisor (e.g., VMware ESX Server™, Microsoft Hyper-V™, etc.). Virtualization softwares provide functionality to disassociate virtual machines from the underlying hardware by providing virtualized devices and resources to virtual machines. For example, a virtual machine is provided with a virtual disk, which appears to the operating system or applications running in the virtual machine as a real hard drive. 
     A virtual disk can be configured to be a thin virtual disk or a thick virtual disk. In case of a thick virtual disk of a certain size, the virtualization software allocates the full amount of storage in the underlying real hard drive or any other type of underlying physical storage. For example, if a virtual disk is configured to be of size 10 GB, full 10 GB space is allocated in the underlying physical storage right in the beginning. On the other hand, in case of a thin virtual disk of size 10 GB (for example), the virtualization software typically allocates a small storage to begin with, in the underlying physical storage. More physical storage is allocated to the thin virtual disk as needed. Hence a thin virtual disk can provide space savings on a physical disk or storage because the actual physical space occupied by a think disk generally includes only those blocks that have been written at least once since the virtual disk&#39;s creation. 
     Unfortunately, guest software running inside of a virtual machine using thin virtual disks can negate those space savings by writing temporary data. When this data is written to a block location never written before, it causes the thin virtual disk to grow in size. Later, when the guest software deletes the data, the thin disk does not shrink because the thin disk is unaware that the blocks are no longer used by the guest. This behavior can therefore cause thin disks to occupy more space on physical disks or storage than they need to occupy. 
     SUMMARY 
     In one embodiment, a method of making a virtual machine space efficient is disclosed. The virtual machine includes a virtual disk. The method includes creating a temporary virtual disk and adding the temporary virtual disk to the virtual machine. The temporary virtual disk works in conjunction with the virtual disk. The guest software (e.g., applications and operating system) running in the virtual machine is configured to store temporary files in the file system of the temporary virtual disk. 
     In another embodiment, a virtualization system is disclosed. The virtualization system includes a host having a physical disk drive and a hypervisor running on the host and hosting a virtual machine. A virtual disk is associated with the virtual machine. A temporary virtual disk is also associated with the virtual machine. The guest software (e.g., applications and operating system) running in the virtual machine is configured to write temporary files associated with applications running in the virtual machine, in to the file system of the temporary virtual disk and not into the file system of the virtual disk. 
     In yet another embodiment, a computer readable media having programming instruction for making a virtual machine space efficient is disclosed. The virtual machine includes a virtual disk. The computer readable media includes programming instructions for creating a temporary virtual disk and programming instructions for adding the temporary virtual disk to the virtual machine. The temporary virtual disk works in conjunction with the virtual disk. The computer readable media further includes programming instructions for configuring the software running in the virtual machine to store temporary files in the file system of the temporary virtual disk. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a logical diagram of a virtual machine, a virtual disk and a physical disk. 
         FIG. 2  illustrates a logical diagram of a virtual machine configured to use more than one virtual disks in accordance with one or more embodiments of the present invention. 
         FIG. 3  illustrates a flow diagram of configuring a virtual machine to use a temporary virtual disk for storing temporary files in accordance with one or more embodiments the present invention. 
         FIGS. 4A and 4B  illustrate a method for adding a temporary virtual disk in a virtual machine in accordance with one or more embodiments the present invention. 
         FIG. 5  illustrates a logical diagram of a system including a redirecting file system driver in accordance with one or more embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a logical arrangement of a physical disk  106 , a virtual disk  102  and a virtual machine  100 . A virtual machine runs in a virtualized environment which is generally created by installing a hypervisor on a physical host. A virtual machine uses virtual devices and hardware such as a virtual processor, virtual network interface card, virtual disk, etc. These virtualization details are well known in the art, hence a detailed discussion is being omitted. 
     Virtual machine  100  uses virtual disk  102 , which is viewed as a normal storage disk by guest software (such as an operating system  112  and applications  110 ) running in virtual machine  100 . Virtual disk  102  includes virtual blocks  104 , which are used by applications or operating system running in virtual machine  100  to store file data. These virtual blocks  104  represent storage space in virtual disk  102 . In one embodiment, a virtual disk provides normal file system capabilities to applications running in virtual machine  100 . However, the virtual disk itself may be stored as a single file in physical disk  106 . In other embodiment, virtual disk  102  may be stored on physical disk  106  in multiple files form. 
     When guest software stores data in virtual blocks  104  of virtual disk  102  (which appears to be a normal storage device to guest software), through file system  114 , the previously unused virtual blocks are marked as “used.” To store this data in physical blocks  108  in physical disk  106 , more physical blocks are allocated for data by host file system  116 . When guest software deletes some data, file system  114  marks corresponding virtual blocks as unused. However, host file system  116  remains unaware of this reclamation of virtual blocks by guest software. Hence, host file system continues treating the underlying corresponding physical blocks as “used.” Hence, the size of virtual disk  102  as stored in physical disk  106  does not shrink. 
       FIG. 2  illustrates a logical diagram of virtual machine  100  configured to use more than one virtual disks  102 ,  102 T. Virtual disk  102 T has its own file system  114 ′. Applications and operating system (i.e., guest software) running in virtual machine  100  create temporary files for the duration of a session and then either delete these temporary files or don&#39;t use these files during the next session. However, since host file system  116  remains unaware of these file deletions (because file system  114  marks virtual blocks unused but the status of corresponding physical blocks remain the same), the size of virtual disk  102  in physical disk  106  does not shrink. Over the period of time in which virtual disk  102  remains in use, the size occupied by virtual disk  102  on physical disk  106  continues to grow. Temporary files are files that are created and used by guest software during one power-on session only. 
     In one embodiment, virtual machine  100  is configured to use more than one virtual disks. A temporary virtual disk  102 T is created every time virtual machine  100  is started. Temporary virtual disk  102 T is configured to be used for storing temporary files. When virtual machine  100  shuts down or powered off, temporary virtual disk  102 T is deleted. 
     A virtual disk is composed of one or more files. Taking at least one snapshot results in one base disk and one or more delta disk files. In another embodiment, a snapshot of temporary virtual machine  102 T is taken upon power-on of virtual machine  100 , thereby creating a delta disk (or redo log file). A snapshot of a virtual disk is typically taken to preserve the state of the virtual disk so the virtual disk can be reverted back the same state at a later time. In one embodiment, this delta disk is deleted during power off. In other words, the snapshot is reverted back to its original state during powering off. In another embodiment, the delta disk is preserved upon a power off operation and continues to persist until a user explicitly reverts the virtual disk back to its original state. During the powered on period of virtual machine  100  any “write” to temporary virtual disk  102 T is routed to the delta disk. Hence, temporary files are written to this delta delta disk. The term “non-persistent” means that the information saved in the disk is lost when virtual machine  100  is powered off. 
       FIG. 3  illustrates a process  200  of adding a temporary virtual disk to a virtual machine. At step  202 , a new virtual disk is created. Various virtualization infrastructure providers (for example, VMware, Microsoft, etc.) provide tools, APIs and methods for creating new virtual disk files. For example, VMware Workstation™ product provides a wizard (Add-&gt;New Hard Disk-&gt;Create a New Virtual Disk) to add a new virtual disk to a virtual machine. At step  204 , virtual machine configurations are modified to enable the virtual machine to see this newly added virtual disk. At step  206 , the newly created virtual disk is formatted. Disk formatting means creating an empty file system on the disk. With a host file system compatible with guest software, at step  208 , the newly created virtual disk is set to be non-persistent. Alternatively, if the underlying platform or virtualization system does not provide functionality to create non-persistent virtual drives, this step may be omitted and process  200  may be repeated every time virtual machine starts. However, if a virtualization platform provides this functionality of creating non-persistent virtual drives, then process  200  only needs to be performed once for a particular virtual machine. 
     At step  210 , applications and guest operating system running in virtual machine  100  are configured to store temporary files in the file system on the newly added temporary virtual disk. In one embodiment, environment variables such as TEMP and TMP (in the case of Microsoft Windows™) may be changed to store temporary files in the file system on the temporary virtual disk (for example, by changing the value of the % TEMP % environment variable c:\temp to d:\temp, wherein drive letter c refers to the file system on the main virtual disk and d to the file system on the temporary virtual disk). In other embodiments, symbolic/hard linking, or folder redirection mechanism may be employed to route temporary file creation to the temporary virtual disk. 
       FIG. 4A  illustrates creating and adding a temporary virtual disk to virtual machine  100 , in a preferred embodiment. When a temporary and non-persistent virtual disk  102 T is added to virtual machine  100 , virtual machine  100  creates a snapshot of non-persistent temporary virtual disk  102 T at startup. As a result of taking the snapshot operation, a delta disk file  102 F 1  of base disk  102 F is created and all subsequent writes to non-persistent temporary virtual disk  102 T are routed to delta disk  102 F 1 . If non-persistent temporary disk  102 T is configured in the “non-persistent mode,” this delta virtual disk  102 F 1  is automatically discarded when virtual machine  100  is powered off. In one embodiment, the size of base disk file  102 F is kept at the minimum at the time of its creation. Since a snapshot is created every time virtual machine  100  is started, base disk file  102 F is not used for write operations, and hence base disk file  102 F does not grow in size. 
       FIG. 4B  illustrates a process  300  of creating a delta disk for storing temporary files. At step  302 , a request for powering on a virtual machine is entertained. At step  304 , a delta disk is created for storing temporary files during the power-on session of the virtual machine. At step  306 , the virtual machine is powered on. At step  308 , guest software runs and uses the delta disk for storing temporary files. At step  310 , the virtual machine is powered off. At step  312 , the delta disk is deleted. 
       FIG. 5  illustrates  FIG. 2  in another embodiment. A redirecting file system driver  120  is inserted between virtual machine  100  and virtual disks  102 ,  102 T. With redirecting file system driver  120  monitoring write operations to file systems, step  210  of process  200  ( FIG. 3 ) does not need to be performed in this embodiment. In one embodiment, all file operations go through redirecting file system driver  120 . Redirecting file system driver  120  is configured to separate out temporary file data and automatically send this temporary file data to temporary virtual disk  102 T, without a need to configure the guest operating system and applications in virtual machine  100 . In one embodiment redirecting file system driver  120  is a part of a file system driver. In another embodiment redirecting file system driver  120  exists separately from the file system driver and is loaded when the file system driver is loaded. When this temporary file data is needed by guest software, redirecting file system driver  120  automatically redirects read operations to temporary virtual disk  102 T. 
     With the above embodiments in mind, it should be understood that the invention can employ various computer-implemented operations involving data stored in computer systems. These operations are those requiring physical manipulation of physical quantities. Any of the operations described herein that form part of the invention are useful machine operations. The invention also relates to a device or an apparatus for performing these operations. In one embodiment, the apparatus can be specially constructed for the required purpose (e.g. a special purpose machine), or the apparatus can be a general-purpose computer selectively activated or configured by a computer program stored in the computer. In particular, various general-purpose machines can be used with computer programs written in accordance with the teachings herein, or it may be more convenient to construct a more specialized apparatus to perform the required operations. 
     The embodiments of the present invention can also be defined as a machine that transforms data from one state to another state. The transformed data can be saved to storage and then manipulated by a processor. The processor thus transforms the data from one thing to another. Still further, the methods can be processed by one or more machines or processors that can be connected over a network. The machines can also be virtualized to provide physical access to storage and processing power to one or more users, servers, or clients. Thus, the virtualized system should be considered a machine that can operate as one or more general purpose machines or be configured as a special purpose machine. Each machine, or virtual representation of a machine, can transform data from one state or thing to another, and can also process data, save data to storage, display the result, or communicate the result to another machine. 
     The invention can also be embodied as computer readable code on a computer readable medium. The computer readable medium is any data storage device that can store data, which can thereafter be read by a computer system. Examples of the computer readable medium include hard drives, network attached storage (NAS), read-only memory, random-access memory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes and other optical and non-optical data storage devices. The computer readable medium can include computer readable tangible medium distributed over a network-coupled computer system so that the computer readable code is stored and executed in a distributed fashion. 
     Although the method operations were described in a specific order, it should be understood that other housekeeping operations may be performed in between operations, or operations may be adjusted so that they occur at slightly different times, or may be distributed in a system which allows the occurrence of the processing operations at various intervals associated with the processing, as long as the processing of the overlay operations are performed in the desired way. 
     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications can be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.