First published on TECHNET on Jul 14, 2006
We’ve heard a lot of feedback recently from beta testers regarding the loss of restore points caused by dual-booting Windows XP. We’d like to explain the reasons behind this behavior, the impact on various recovery features, and why a backported fix is not currently planned for Windows XP.
The problem
: Windows XP automounts every disk it detects, including external or removable hard disks. As part of the automounting process, NTFS writes to the disk, and these writes are detected by the volsnap.sys driver in Windows XP. Because this version of volsnap.sys does not recognize the persistent shadow copies (also known as restore points) made by the volsnap.sys driver in Windows Vista, Windows XP cannot maintain the integrity of the shadow copy storage area and deletes the shadow copies to avoid corrupting them. Note that dual-booting Windows Vista with Windows Server 2003 or Windows XP Professional x64 Edition will also result in the shadow copies being deleted.
The impact
: When you boot into Windows XP and automount a disk, you will notice the following effects on the disk after booting back to Windows Vista:
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All restore points are deleted from the disk.
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All previous versions of files are deleted from the disk.
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All but the most recent CompletePC Backup are deleted from the disk. The remaining backup made by CompletePC Backup is full and complete and can be used to restore your entire computer.
File backups are not affected because these backups do not rely on restore points.
Why this fix is not trivial for Windows XP
: Backporting volsnap.sys to Windows XP would require significant development and testing time. The entire Volume Shadowcopy Service (VSS) subsystem in Windows Server 2003, Windows Vista, and Windows Server “Longhorn” would need to be backported to Windows XP and would likely break a number of third-party backup applications that rely on the current version of volsnap.sys in Windows XP.
The workaround
: To avoid losing Windows Vista shadow copies on a disk that you don’t need to access from Windows XP, disconnect or power off the disk prior to booting to Windows XP.
