What Happens when Disk Contents Change During a Backup?

Discussion in 'Acronis True Image Product Line' started by BritGeek, Jul 30, 2005.

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  1. BritGeek

    BritGeek Guest

    I'm wondering what happens when the disk contents change during a backup.

    For instance, suppose True Image has already copied the sectors for Outlook.pst to the backup image, then I receive a new email so Outlook writes to that file. Does True Image somehow keep track of what sectors are updated during the backup then go back later and re-write them to the image? Or, will the backup image just contain the old copy of Outlook.pst that doesn't contain that new email?

    Now for a worse situation - what happens if True Image has backed up half the sectors of a file and then an application writes to that file? Do I end up with a corrupt file in the backup? How does True Image handle this? Does it lock files while it is writing them? If so, what if the file is already locked by an application?

    I'm asking these things because:
    1) I'm a geek and I like to know how things work.
    2) I need to know if it's best to shut down all applications while the backup is in progress, or whether it's safe to keep working.
  2. wdormann

    wdormann Registered Member

    Jun 27, 2004
    This press release should answer your questions.

    In a nutshell, once the backup starts, any filesystem changes will no go into the image. It behaves as if a "snapshot" is taken of the drive at the instant you begin imaging.
  3. BritGeek

    BritGeek Guest

    Thanks, that article answered my questions, it's written by Acronis' director of engineering so he should know what he's talking about.

    Still, I think I'll disable my defragger [DiskKeeper, which runs in the background whenever it feels like it] while I'm creating an image :)

    Even if True Image can theoretically handle this, it would sure make it create a huge buffer of snapshot sectors.
  4. Acronis Support

    Acronis Support Acronis Support Staff

    Apr 28, 2004
    Hello BritGeek,

    Thank you for your interest in Acronis Disk Backup Software.

    Acronis True Image 8.0 is the complete backup and disaster recovery solution -
    you can create an image of your entire configuration on a live system
    so you never need to shut-down to create an image.

    The Acronis True Image 8.0 program uses a special method of "snapshot"
    image creation, it doesn't store the standalone files or directories,
    but saves blocks of your hard drive data, saving the information about the
    disk/partition geometry.

    After the restore you will get the an exact copy of once backed up partition,
    you will not need to reinstall anything.

    Once Acronis True Image initializes the backup process of a volume (which logically corresponds to a single partition, if there are no Dynamic Disks), Acronis Snapshot Manager flushes the file system mounted to that volume temporarily freezing all the operations on the system volume. Immediately thereafter, the Snapshot Manager driver creates a point-in-time view of the system volume and a bitmap describing the used sectors on this volume. Once the bitmap is created, the filter driver unfreezes the I/O operations on the system volume. It generally takes just several seconds to create a point-in-time view of the volume. After that, the operating system continues working as the imaging process is under way.

    Acronis True Image 8.0 reads the sectors on the system volume according to the created bitmap. Once a sector is read, the appropriate bit in the bitmap is reset. In its turn, the Acronis driver continues working to hold the point-in-time view of the system volume. Whenever the driver sees a write operation directed at the system volume, it checks whether these sectors are already backed-up, if they are not, the driver saves the data on the sectors that will be overwritten to a special buffer created by the software, then it allows the sectors to be overwritten. Acronis True Image backs up the sectors from the special buffer, so that all the sectors of the point-in-time view of the system volume will be backed up intact. Meanwhile, the operating system continues working as usual.

    If you have complex applications such as Microsoft SQL Server, Oracle or Microsoft Exchange running on your machine then please read the following FAQ article describing the issue: http://www.acronis.com/enterprise/products/ATISWin/faq.html#19

    I recommend you to download and install the free trial version to see how the software works on your computer.

    The trial version of Acronis True Image 8.0 is available at:

    You can also find more information on how to use this software in Acronis True Image 8.0 User's Guide which is available at: http://www.acronis.com/homecomputing/download/docs/

    Thank you.
    Alexey Popov
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