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?


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
  • 1
    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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