Juan87

MICROSOFT CORPORATION
VHDX Format Specification
Version 0.95
25-April-2012

© 2012 Microsoft Corporation. All rights reserved.This specification is provided under the Microsoft Open Specification Promise. For further details on the Microsoft Open Specification Promise, please refer to: http://www.microsoft.com/interop/osp/default.mspx.Microsoft may have patents, patent applications,trademarks, copyrights, or other intellectual property rights covering subject matter in these materials. Except as expressly provided in the Microsoft Open Specification Promise, the furnishing of these materials does not give you any license to these patents, trademarks, copyrights, or other intellectual property. |

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Table of Contents
1 Introduction 7
1.1 Concepts 7
1.2 Common Acronyms 8
1.3 Specific Terminology 9
1.4 Conventions 9
2 VHDX Format 10
2.1 Features and Benefits 10
2.2 Layout 10
2.3 Header Section 12
2.4 Log12
2.5 Blocks 12
2.6 BAT 13
2.7 Metadata Region 13
3 Detailed Specification 14
3.1 Header Section 14
3.1.1 File Type Identifier 14
3.1.2 Headers 14
3.1.3 Region Table 17
3.2 Log 18
3.2.1 Log Entry 19
3.2.2 Log Sequence 22
3.2.3 Log Replay 22
3.3 Blocks 24
3.4 BAT 24
3.4.1 BAT Entry 25
3.5 Metadata Region 29
3.5.1 Metadata Table 30
3.5.2 Known Metadata Items 31
4 Appendix 36
4.1Globally Unique Identifiers (GUIDs) 36
4.2 CRC-32C 36
5 Documentation Change History 37

List of Structures
Structure 1: File Type Identifier 14
Structure 2: Header 15
Structure 3: Region Table Header 17
Structure 4: Region Table Entry 17
Structure 5: Log Entry Header 20
Structure 6: Log Zero Descriptor 21
Structure 7: Log Data Descriptor 21
Structure 8: Log Data Sector 22
Structure9: BAT Entry 25
Structure 10: Metadata Table Header 30
Structure 11: Metadata Table Entry 30
Structure 12: File Parameters Metadata Item 31
Structure 13: Virtual Disk Size Metadata Item 32
Structure 14: Page 83 Data Metadata Item 32
Structure 15: Logical Sector Size Metadata Item 32
Structure 16: Logical Sector Size Metadata Item 33
Structure 17: Parent Locator Header 33
Structure 18:Parent Locator Entry 33

List of Figures
Figure 1: Logical Layout 11
Figure 2: File Layout Example 11
Figure 3: Header Section Layout 14
Figure 4: Log Layout Example 18
Figure 5: Log Entry Structure Layout Example 19
Figure 6: BAT Layout Example 24
Figure 7: Metadata Region Layout Example 29


List of Tables
Table 1: Concepts 7
Table 2: Acronyms 8
Table 3: Terminology 9
Table 4:Known Region Properties 18
Table 5: Payload BAT Entry States 26
Table 6: Sector Bitmap BAT Entry States 28
Table 7: Known Metadata Item Properties 31
Table 8: VHDX Parent Locator Entries 34

Introduction
This paper describes the VHDX virtual hard disk format that provides a disk-in-a-file abstraction. This document is written to help guide development of VHDX virtual hard disk formatimplementations that are compatible with those provided by Microsoft.
This specification assumes that you are familiar with hard disk technologies, including how hard disks interface with the operating system or a virtual machine and understand how data is accessed and laid out on the physical medium.
Concepts
This specification uses certain disk technology concepts that are detailed below.
Table 1:Concepts
Concept | Explanation |
Host volume or disk | The volume or disk on which the virtual hard disk file resides. |
Logical sector size | The minimum required alignment of IO to a disk. The disk cannot handle IO that is aligned to an offset that is not a multiple of the logical sector size. The logical sector size for the virtual hard disk and host disk could differ. |
Physical sector...