Making TrueImages Smaller

Discussion in 'Acronis True Image Product Line' started by CAOgdin, Mar 5, 2007.

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  1. CAOgdin

    CAOgdin Registered Member

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    I use ATI at lots of sites, and some of them make very big files (or collections of files, if you use archive splitting).

    One of the sources of that size is the non-zero, unused sectors on the partition being backed up. If you can zero out all the unused space, ATI gets a lot more efficient. I recently gained a 19% REDUCTION in total produced image size by zeroing out unused space on a partition.

    WISH LIST: Give me the option (preferably by partition, but acceptable as a global option) to not record empty space. For integrity, of course, each block of sectors that are not reserved in the file system would have to be "simulated" in the compression, either by a specification of the sectors in the cluster, or by non-monotonic recording of the sector number of each new image segment. So, you can't get 100% compression of unused space, but you can get close on a well-defragmented drive/partition.

    IN THE MEANTIME: Go get "Disk Redactor" at http://www.cezeo.com/products/disk-redactor/ and run it. You'll see an immediate reduction in produced image size from your next ATI run, but not as much as I'd expect (for a system that provides 50% compression, and 5 GB on a 10 GB partition, I'd expect the final ATI size to be about 2.5GB plus a small amount of "accounting overhead")...maybe 60% of the actual "occupied" space on a partition).

    I am now looking for a command-line version of Disk Redactor that I can incorporate into my script for pre-image command (see Pre/Post Commands in the Tools | Options menu). That will zero out all unallocated space immediately before I create an Image.

    --Carol Anne
     
  2. foghorne

    foghorne Registered Member

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    I was under the impression that ATI only recorded UNused sectors when it was operating raw mode.

    There is no way you can make an generalised estimate like this without understanding the nature of the file formats you are compressing. For example if your 5GB was made up of ready compressed data (jpg/png/mp3 etc) you might actually see an increase and end up with an image which is more than 5GB. Any estimates quoted within TI should be treated as finger-in-the-air guesses and should not be relied upon.

    F.
     
    Last edited: Mar 6, 2007
  3. jp10558

    jp10558 Registered Member

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    Why is Acronis doing sector by sector imaging anyway? For the majority of filesystems, I see it doing file based images, so it only copies over the actual files... Second, I'd suggest also looking into Eraser as an OSS disk wiper.
     
  4. shieber

    shieber Registered Member

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    Sector copying allows it work in background and copy OS files even while the OS is running. Since unused sectors would be a waste of space (nothing ot write to those sectors on a restore, there's little point is copying them in the backup.
     
  5. seekforever

    seekforever Registered Member

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    I don't know if this is just a question of semantics but I only use TI for used-sector imaging of the OS. I do not use it for file-based backups which is what I consider the TI Files and Folders option to be.

    Reason why images: I want to restore a bootable OS, I want it very fast (compared to a file-based backup) and I do not consider dumping data files into a giant container to be the most reliable and convenient way of backing up data files.
     
  6. foghorne

    foghorne Registered Member

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    Not true according to my tests. It appears that TI uses the file interface to identify the file (and the start of the chain) and then uses sector copying to read the file. As schieber hinted, this is how locked files can be copied.

    I have tried this by holding a read/write lock open on a file and then getting TI to back it up. It backed up fine even though the file was locked - this is not going to happen through the file interface.

    F.
     
    Last edited: Mar 6, 2007
  7. CAOgdin

    CAOgdin Registered Member

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    Re: Making Estimates (see 'foghorne' above)

    I respectfully disagree with your assessment. In over many years of making backups with at least 100 different products, there are some generalizations I believe I can safely make.

    The first is that a 50% reduction in size with effective compression is a reasonable heuristic for entire systems with both code and a wide mix of data types. In unique situations, the results can be content-dependent, although programs generally compress more poorly than data files. In some cases (e.g., object-oriented databases) compression can result in 90% reduction (i.e., 10% of the original).

    Second, I believe that your assertion that one must know "...the nature of the file formats you are compressing" is not true in general. Yes, if your partition consists of only MP3 files...already highly compressed...you'll not gain much. I take avantage of that when I copy ATI images to tape: I disable compression, because that's already been done; there is no net gain through additional compression and, as you point out, it can actually be counterproductive.

    Third, your belief "...that ATI only recorded UNused sectors when it was operating raw mode" does not appear to be substantiated in practice. Here's how I tested: I have two partitions on a live XP Pro system. I used ATI WS 9.1 to image them, and resulted in 10.4 GB in ATI output. Then, I immediately ran Disk Redactor, and ran exactly the same configuration of ATI again. And the ATI output was 8.41 GB. The sole difference was having zeroed-out the free space. If you know how to achieve those kinds of results with a change in ATI configuration, I'd be most appreciative. The extra zeroing-out step is one I'd love to avoid.
     
  8. MudCrab

    MudCrab Imaging Specialist

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    Re: Making Estimates (see 'foghorne' above)

    CAOgdin:

    Are you saying that you have to zero-out the free space on the hard drive (or partition) you're backing up every time before you backup?

    In other words, if you reboot Windows, use it normally for a day and run the backup again, does the resulting image once again come out at 10.4GB or does it stay at 8.41GB?

    I'm also curious how this affects large backups. The examples you've shown are very small images. What happens on a backup of 60GB of used space on a primary XP partition?

    Also, I respectfully disagree with you're general assumption of 50% compression. In my many years of backing up, I've found it to be good to a backup 80-90% of the original size. I backup all kinds of program, data, dBase files, etc. and the only ones that compress highly are the dBase files (they usually get 90-95% compression).
     
  9. dantz

    dantz Registered Member

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    Re: Making Estimates (see 'foghorne' above)

    Your results are rather surprising, as I wouldn't expect a free space wipe to make any difference to an imaging program that normally bypasses free space anyway.

    Please check this if you haven't already done so: After running Disk Redacter, does your source partition still contain exactly the same number of bytes of used space and free space?

    Just shooting off the top of my head here, but maybe the free space wipe is reducing the size of the MFT or is at least making it more compressible to ATI during imaging operations.

    I guess it's going to take some testing to figure this one out.
     
  10. foghorne

    foghorne Registered Member

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    Re: Making Estimates (see 'foghorne' above)

    ;)
    I didn't realise the backup market was so flooded ;)

    Err, no. It's a guess. You need to define what you mean by "effective", "entire" and "wide", and by the way "code" is "data". If the data is already compressed you are not going to reach 50%


    I think you are just agreeing with me here. ;)


    So what are you saying, that ATI records all sectors, used or unused?.
    What was the size of the original data? I will be checking for 50% compression :D

    I am puzzled that in your post you don't qualify your statements based on different levels of compression (in the case of ATI) - do they all achieve 50%? or by relating your findings to particular compression algorithms, all you mention is that they are "effective".

    Many in this forum have been backing up with compression for years and are well aware how compression ratios can vary, I think you are up to mischief in your post :rolleyes:


    F.
     
    Last edited: Mar 7, 2007
  11. aggronix

    aggronix Registered Member

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    I wondered about the behavior of ATI and made a little 10 minutes test, too.

    At first I created an image of my 1GB NT Boot Partition. The image file has about 380 MB. I restored this image to unused space to get an exact copy of my partition. Now I've booted NT and deleted all files on the copy but 30 MB or so. I made a new image again.

    The first image file had 380 MB, the second (of the nearly empty partition) has 6 MB.

    Conclusion: ATI does not record empty space, does it? ;)

    aggronix.
     
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