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Under Windows 7, restore points are now basically incorporated in the Volume Shadowing Subsystem. I have heard defragmentation (including the one provided by Windows 7) has the possibility of interfering with the VSS process possibly causing corrupted/incomplete VSS images meaning corrupted/incomplete restore points.

Looking at many of the defraggers around the network, I don't see any of them discussing how their package will not interfere with VSS. Thus I am left to conclude using defraggers might be problematic to future system recovery efforts and I definitely want to avoid that.

So should I forget defragmenting altogether?

One other thought, would using an off-line defragmentation mode of the boot drive prevent VSS interference?

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up vote 4 down vote accepted

No, (online) defrag programs differ only in the heuristics they use to pack the data on disk. The actual moving of blocks is done by calling into the Windows defrag APIs. The defrag API is VSS-aware, and will safely handle snapshots and other advanced NTFS features.

It is actually more dangerous to use an offline defragger, as you are now entrusting the integrity of the NTFS filesystem to third-party code that may not understand all the features of NTFS. By using an online defragger, you guarantee that the defrag itself is done using Microsoft code, no matter which company wrote the defragger.

Incidentally, System Restore was also implemented in Windows Vista using VSS. So it's not new to Windows 7. Whatever you did for defrag on Vista, it'll be the same on Windows 7.

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Then why do the higher end defragers have a VSS operation mode? – mdpc Jan 29 '13 at 21:08
As explained in the documentation for Diskeeper: "When the VSS defragmentation option is enabled, Diskeeper uses proprietary defragmentation engines to help reduce the chance of the defragmentation operation causing new VSS snapshots from being created, thus potentially preventing older snapshots from being purged. In order to do this, the VSS defragmentation engines use more conservative file movement algorithms, which can result in slightly less thorough defragmentation of the volume." – taoyue Jan 29 '13 at 21:12
@taoyue: So then doesn't that mean the answer is "yes"? Isn't there a a chance defragmentation will cause snapshots to be purged? Otherwise, what sense is the feature? – David Schwartz Jan 29 '13 at 21:16
@David Schwartz: The OP asked about "corrupted/incomplete VSS images meaning corrupted/incomplete restore points." Defragmentation does not cause any corruption of existing VSS images. It may, however, trigger the creation of a new snapshot -- which may cause the oldest snapshot to be deleted if you've already hit the limit on VSS disk space usage. If you absolutely must preserve the snapshot taken on the day you installed Windows, then turning off defrag will not achieve this, because just using the computer might evict the oldest snapshot. You need to move the snapshots off the disk. – taoyue Jan 29 '13 at 21:36

In regards to your post, I defrag my computers on a schedule every Wednesday @ 1:00 am and I have never had any issues relating to system restore points, or the volume shadow system. If it were an issue, I think MS would have gone to greater lengths to 'hide' the disk defrag utility.

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Well I did some defragmentation and lost my ability recently to recover any of the restore points on a Windows 7 system. BTW, M$ has a fair number of articles on the subject. – mdpc Jan 29 '13 at 21:04
After doing i bet more research it appears you are right. However, as taoyue noted, the defrag process isn't responsible for there removal, that is a background process. So a defrag shouldn't be directly responsible for lost restore points. Also, relying on restore points isn't really a backup strategy :\ – Lee Harrison Jan 29 '13 at 21:54
And considering that Microsoft's included "disk optimizer" is virtually worthless, this isn't saying a whole lot. – Michael Hampton Jan 29 '13 at 23:28

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