Is an Acronis Image backup really an image?

Discussion in 'Acronis True Image Product Line' started by ddraper, Nov 19, 2008.

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  1. ddraper

    ddraper Registered Member

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    I have always been under the impression that an image backup was bit-by-bit (or binary) copy of the hard-drive. This type of backup was performed without the concept of files but rather as chucks of disk areas and therefore restores were guaranteed to put the disk back the same as before as a binary duplicate.

    So if the *.BAK file extension exclusion settings in TI 2009 can cause specific files to NOT be backed up and thus corrupt Office installations (the infamous TI2009/Office issue), then is it really creating a true file-less image or it is just backing up all of the files on the entire disk into a single TIB file?

    I remember an issue with differential backups using Symantec Ghost where it would often result in a full image being created because so many sectors on the disk had changed? Although aggrevating, it made sense and at least I felt the image was a true binary image.

    Can anyone clarify exactly how Acronis TI does a full image (My Computer) backup? Is it simply copying all of the files into the TIB and if not, then how does it know about the files to the point it can exclude them extension? Apologies if this has already been answered (probably has) and if so could you point me to it.

    I have ALWAYS assumed that the file extension exclusions in TI only applied to FILE based backups and not image backups. But again, this does not appear to be the case. Thanks in advance for clarifying how this works to me and perhaps others on this subject.

    Regards,
    Don
     
  2. seekforever

    seekforever Registered Member

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    First of all, IMO, file exclusions have no place in disk/partition images but I think a lot of people requested that exclusions be possible.

    I have mine setup so there are no exclusions other than the usual pagefile and any hibernation files because they are recreated on bootup anyway.

    True Image does not do a bit by bit copy to the archive. It actually does use the file system to a limited extent and a bitmap to determine changed sectors. The file system activity is fairly small so the image backup is a lot faster than running through the normal file system for access such as in a "data" file (Files and Folders) backup.

    TI, unless requested, only backs up the in-use sectors and when it restores it does not necessarily put the contents of sector ABCD back into ABCD. In this regard, it is not a true image but the file system is adjusted and the user wouldn't know any different.

    If the contents of a sector are moved to a different location such as in defragging then imaging programs like TI see it as a change even if the contents of the overall file remain the same. This is why incrementals and differentials can get large if a defrag has run between the last backup and the incremental/differential. Always defrag then do a Full to avoid this and turn off any auto-defragging between fulls.
     
  3. alan_b

    alan_b Registered Member

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    seekforever, would this explain my query at
    https://www.wilderssecurity.com/showthread.php?t=225451
    I was surprised to find that when "identical" files were imaged before and after NTFS compression, the Acronis image was 74 MBytes larger when C:\ had been reduced by 340 MBytes.

    I thought Windows uncompressed the files before Acronis got them, and the Acronis image should be the same size regardless.
    I have been concerned that I might be doing something wrong, or that there was a way to avoid this bloat.
    Does Acronis actually "snatch sectors behind Windows back" and therefore struggle to compact not only information that is already compressed, but also additionally a NTFS form of dictionary that will be needed by Windows for decompressing ?
    N.B. by "form of dictionary" I am referring to ancient ZIP technology, and I mean whatever equivalent techniques may apply to modern NTFS, which "hurts my brain" !!!

    p.s. In some forum I read that there was no point trying to defrag free space, because creating a Ghost image and immediately restoring it would automatically put all the files at one end, and all the free space at the other.
    I was very pleasantly surprised to find an Acronis image gives the same benefit, and pushed me towards belief that files and not sectors were backed up.

    Regards
    Alan
     
  4. tonyseeking

    tonyseeking Former Poster

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    Define "image"
     
  5. shieber

    shieber Registered Member

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    Not sure why anyone would want to make copies of empty sectors. If one was doing exact track by track, bit by bit copies, one could only restore to the same size hdisk with the same physical format, all for the sake of empty sectors? Why?

    I do understand that with certain nonstandard disk layouts, for example on CDs and DVDs, make exact clones is useful at defeating the copy protection schemes, but other than that . . .
     
  6. seekforever

    seekforever Registered Member

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    I had read your original post before but I can't offer any explanation for what you are seeing because I just don't know just how TI and NTFS does their respective parts in puzzle.
     
  7. ddraper

    ddraper Registered Member

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    Good question. I was referring to an "identical image" where an image is an exact replica of the original disk contents bit-for-bit. I you take a picture with a digital camera and change one pixel, it is no longer an "identical" image.

    Thanks for the replies as this was very helpful and informative. So the answer to my question is no, it does not make an exact image. So a full Acronis backup is an image but not an exact physical replica of the original but perhaps a logical replica as the OS does not detect a difference. What you have upon restore is not what you started with but works the same for practical purposes. This explains how file exclusions can be included in a full image backup. I actually thought the file exclusion did not apply at all in a full backup so my assumptions have been wrong for a while.

    And it makes sense that doing a file-by-file backup as most most other backup programs are limited to is a more intensive task taking significantly more time. Thanks again for education. I feel better....I think!

    I do know that compression of already compressed data can often result in larger output rather than smaller. Therefore, I might guess that Acronis istrying to compress data that is already compressed (the compressed NTFS volumne) resulting in an larger than image than before. Just a guess.

    Don
     
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