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On Windows 7 I am creating a system image of the system drive (C: in my case) onto an external USB harddisk. The process is taking long (has been running for an hour now).

My question: I am taking care not to make any changes to the C: drive while the system image is being created (i.e. I am not creating any files on the desktop, etc.). But surely, there will be changes to the system drive, because I am accessing the web and therefore, the browser is updating its cache, etc. How does Windows maintain consistency during the image create operation? Am I being overly cautious by not creating any files? Or should I not even run a browser while the image create is going on?

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To get an idea of how it's handling open files and files created during the image backup, read up on Windows' Shadow Copy mechanisms, and how they work.

From Microsoft:

The Volume Shadow Copy Service (VSS) is a set of COM interfaces that implements a framework to allow volume backups to be performed while applications on a system continue to write to the volumes.

From Wikipedia:

Shadow Copy (also known as Volume Snapshot Service, Volume Shadow Copy Service or VSS), is a technology included in Microsoft Windows that allows taking manual or automatic backup copies or snapshots of data, even if it has a lock, on a specific volume at a specific point in time over regular intervals.

  • +1 Thank you, will read both sources. But a preliminary feeling I get from your answer and the brief synopses is that consistency is provided for by Windows. Would that be a fair statement? Thanks again. – Sabuncu Dec 9 '13 at 20:00
  • Basically it takes a copy of the file system and backs that up instead of the "live" file system. That way you can have files open a the time. Any system created files created during backup aren't going to matter. User-created files creating during backup should be checked and confirmed they were added to the backup (if that's what's wanted). – Ƭᴇcʜιᴇ007 Dec 9 '13 at 20:03
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    Thank you so much. Not only did I get my answer, also learned the existence of the Shadow Copy technology. This is the best type of answer, where one learns more than what was originally asked. – Sabuncu Dec 9 '13 at 20:09

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