Virtual Disk Storage Techniques

• US 20120278799A1
• Filed: 04/26/2011
• Published: 11/01/2012
• Est. Priority Date: 04/26/2011
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Starks, John A., Green, Dustin L., Harris, Todd William, John, Mathew, Rajaram, Senthil, Traut, Eric
• Granted Patent: US 9,519,496 B2
• Time in Patent Office: Days
• US Class Current: 718/1
• CPC Class Codes: G06F 2009/45583 Memory management, e.g. access or allocation
• CPC Class Codes: G06F 3/061 Improving I/O performance
• CPC Class Codes: G06F 3/0619 in relation to data integrity, e.g. data losses, bit errors
• CPC Class Codes: G06F 3/0643 Management of files
• CPC Class Codes: G06F 3/0644 Management of space entities, e.g. partitions, extents, pools
• CPC Class Codes: G06F 3/0659 Command handling arrangements, e.g. command buffers, queues, command scheduling
• CPC Class Codes: G06F 3/0664 at device level, e.g. emulation of a storage device or system
• CPC Class Codes: G06F 3/0673 Single storage device
• CPC Class Codes: G06F 3/0683 Plurality of storage devices
• CPC Class Codes: G06F 3/0689 Disk arrays, e.g. RAID, JBOD
• CPC Class Codes: G06F 3/121 Facilitating exception or error detection and recovery, e.g. fault, media or consumables depleted
• CPC Class Codes: G06F 9/455 Emulation; Interpretation; Software simulation, e.g. virtualisation or emulation of application or operating system execution engines
• CPC Class Codes: G06F 9/45545 Guest-host, i.e. hypervisor is an application program itself, e.g. VirtualBox
• CPC Class Codes: G06F 9/45558 Hypervisor-specific management and integration aspects

Abstract

In an exemplary embodiment, a virtual disk file can be assigned an identifier and a virtual disk files that is dependent on the virtual disk file can include a copy of the identifier. In the instance that the virtual disk file is opened and data is modified that causes the contents of a virtual disk extent to change the identifier can be changed. If the virtual disk file and the dependent virtual disk file are used to instantiate a virtual disk the difference between identifiers can be detected, which is indicative of the fact that the virtual disk may be corrupted. Other techniques are described in the detailed description, claims, and figures that form a part of this document.

Claims

1. A computer-readable storage medium including instructions that upon execution by a processor cause the processor to:

open a virtual disk file, the virtual disk file including a first unique identifier and virtual disk extent data that forms at least a part of the data in a virtual disk;

overwrite the first unique identifier in the virtual disk file with a second unique identifier in response to detecting an attempt to write information to the virtual disk file that affects how virtual disk extent data is interpreted;

determine that the second unique identifier was written to a persistent copy of the virtual disk file; and

write the information to virtual disk file in response to determining that the second unique identifier was written to the persistent copy of the virtual disk file.

2. The computer-readable storage medium of claim 1, the instructions that upon execution cause the processor to overwrite the first unique identifier further comprising instructions that upon execution cause the processor to:

overwrite the first unique identifier in response to detecting an attempt to write to a bit pattern of a virtual disk extent.

3. The computer-readable storage medium of claim 1, further comprising instructions that upon execution cause the processor to:

deny a request to instantiate the virtual disk in response to a determination that the second unique identifier obtained from the virtual disk file is not equal to a unique identifier stored in a child virtual disk file.

4. The computer-readable storage medium of claim 1, further comprising instructions that upon execution cause the processor to:

change the second unique identifier to the first unique identifier in response to user input.

5. The computer-readable storage medium of claim 1, further comprising instructions that upon execution cause the processor to:

associate a number with information identifying virtual disk extents in a group that are completely described by the child virtual disk file;

update a copy of the number in the child virtual disk file to a second number in response to a determination that data in the virtual disk file was modified; and

update the number associated with the information to the second number in response to a determination that the information accurately reflects the state of the virtual disk extents in the group.

6. The computer-readable storage medium of claim 1, further comprising instructions that upon execution cause the processor to:

access sector bitmaps for a group of virtual disk extents written to a section of the virtual disk file, the section of the virtual disk file having a virtual disk file offset selected such that the section is aligned with sectors of a storage device configured to store the virtual disk file.

7. A computer system, comprising:

a processor; and

a memory, the memory in electronic communication with the processor when powered, the memory including instructions that upon execution by the processor cause the processor to;

instantiate a virtual disk, the virtual disk including a group of virtual disk extents described by a first virtual disk file, the first virtual disk file including a first identifier;

load information identifying virtual disk extents in the group that are completely described by the first virtual disk file into random access memory, the information associated with a copy of the first identifier;

change the first identifier in the first virtual disk file to a second identifier after opening the first virtual disk file; and

change the copy of the first identifier associated with the information to the second identifier in response to a determination that the information accurately reflects the state of the virtual disk extents in the group.

8. The computer system of claim 7, the instructions that upon execution cause the processor to instantiate the virtual disk further comprising instructions that upon execution cause the processor to:

instantiate the virtual disk in response to a determination that a unique identifier in the first virtual disk file matches a unique identifier located in a parent virtual disk file.

9. The computer system of claim 7, the instructions that upon execution cause the processor to instantiate the virtual disk further comprising instructions that upon execution cause the processor to:

deny a request to instantiate the virtual disk in response to a determination that a unique identifier in the first virtual disk file does not match a unique identifier located in a parent virtual disk file.

10. The computer system of claim 7, the instructions that upon execution cause the processor to change the first identifier in the first virtual disk file further comprise instructions that upon execution cause the processor to:

change the first identifier in the first virtual disk file to the second identifier in response to a determination that a virtual disk extent in the group was modified.

11. The computer system of claim 7, the instructions that upon execution cause the processor to change the copy of the first identifier associated with the information further comprise instructions that upon execution cause the processor to:

change the copy of the first identifier associated with information to the second identifier during a procedure to close the virtual disk file.

12. The computer system of claim 7, the instructions that upon execution cause the processor to change the copy of the first identifier associated with the information further comprise instructions that upon execution cause the processor to:

change the copy of the first identifier associated with the information to the second identifier in response to the determination that the virtual disk file was modified; and

log modifications made to the information.

13. The computer system of claim 7, further comprising instructions that upon execution cause the processor to:

access sector bitmaps for the group of virtual disk extents written to a section of the virtual disk file, the section of the virtual disk file having a virtual disk file offset selected such that the section is aligned with sectors of a storage device configured to store the virtual disk file.

14. The computer system of claim 7, further comprising instructions that upon execution cause the processor to:

detect an attempt to modify information in a parent virtual disk file that affects how virtual disk extent data of the virtual disk based on the parent virtual disk file is interpreted, the parent virtual disk file including a first random value;

overwrite the first random value in the parent virtual disk file with a second random value;

flush the virtual disk file; and

modify the information in the parent virtual disk file in response to receipt of a signal indicating that the flush completed.

15. The computer system of claim 7, further comprising instructions that upon execution cause the processor to:

derive updated information in response to a determination that the information is associated with a copy of the first number and the first virtual disk file includes the second number.

16. A computer implemented method, comprising:

opening a parent virtual disk file, the parent virtual disk file being linked to a child virtual disk file, the parent virtual disk file including a first identifier and the child virtual disk file including a copy of the first identifier;

overwriting the first identifier in the virtual disk file with second identifier in response to detecting an attempt to modify data that describes a virtual disk extent;

issuing an input/output job indicative of overwriting the first identifier with the second identifier to a storage device configured to store a persistent copy of the parent virtual disk file;

issuing a flush command to the storage device; and

modifying the data that describes the virtual disk extent in response to receipt of a signal indicating that the storage device persisted the contents of the internal cache.

17. The computer implemented method of claim 16, further comprising:

denying a request to instantiate the virtual disk in response to a determination that the second identifier in the persistent copy of the virtual disk file does not match the first identifier stored in the child virtual disk file.

18. The computer implemented method of claim 16, further comprising:

changing the unique identifier to a previous value in response to user input.

19. The computer implemented method of claim 16, further comprising:

instantiating the virtual disk, the virtual disk including virtual disk extents described by the parent virtual disk file and virtual disk extents described by the child virtual disk file, the child virtual disk file including a sequence number;

loading information identifying a subset of virtual disk extents in the child virtual disk file that are completely described by the child virtual disk file into random access memory, the information associated with a copy of the sequence number;

incrementing the sequence number in the child virtual disk file in response to a determination that the child virtual disk file was modified; and

incrementing the sequence number associated with the information in response to a determination that the information accurately reflects the state of the subset of virtual disk extents in the child virtual disk file.

20. The computer implemented method of claim 16, further comprising:

writing sector bitmaps for a group of virtual disk extents to a section of the virtual disk file, the section of the virtual disk file having a virtual disk file offset selected such that the section is aligned with sectors of a storage device configured to store the virtual disk file.